The following is a representative sample of correspondence received on the subject from various scholars and academics from a variety of backgrounds. The bracketed  words were not in the original communication but have been added for clarification purposes or grammatical flow. None of the communicants have read Svendsen's thesis - although his claims were presented to them. The communicants were asked to comment on whether there was any substantial difference between heõs and heõs hou in regards to the question under consideration.
It should be stressed that while various scholars had varying opinions on whether Mary was perpetually virgin, not ONE academic, of the dozens who replied to the survey, concurred with Svendsen's rule on heõs hou.
"I would suggest that the expression offers no final solution either way. It is not EXCLUDED that Joseph and Mary had sexual relations after the birth of Jesus, but it is not EXCLUDED that they did not. [Raymond] Brown's assessment of the evidence makes that clear. Thus, a double tradition is possible. As far as Matthew 1:25 is concerned, the Roman Catholic (and Orthodox) Church has gone down one direction (and has every right to do so) while many Protestant Traditions have gone done the other (and they have every right to do so). What matters is that we accept the ambiguity of the expression, give a good basis for what we would like to defend ... and then respect those people who - generally for very good Christian reasons (here, often, to see Mary and Joseph in a genuine marriage) - think differently. - Rev. Francis J. Moloney, SDB, AM, STL, SSL, D.Phil., F.A.H.A. (1973), Catholic University, Department of Biblical Studies, School of Religious Studies, Past President of the Catholic Biblical Association.
"The Greek adverb is capable of many nuances, for example, see Zorrell's Lexicon Graecum [Paris, 1961]. In Matthew 1:25, the meaning must take into account the context. Here the evangelist is emphasizing that Joseph is not the biological father of Jesus; this meaning does not imply or suggest that sexual activity took place after the birth of Jesus." - Dr. Edward L. Bode, M.A., S.S.L., S.T.D.
"I have not done the necessary research to align myself with one or the other side in this debate. In general, I am very wary of arguments that depend heavily or exclusively on linguistic or syntactical uses to prove a point. Context is so heavily involved in making meaning that we would be ill-advised to try to establish an ironclad rule for the use of particles--at least unless we had a staggering number of examples." - Dr. Robert F. Hull Jr., M.Div, Ph.D, Professor of New Testament, Emmanuel School of Religion.
"One should always be suspicious of a linguistic argument that is coincidentally being used to further a sectarian position. Omitting LXX texts from consideration is especially arbitrary. It seems an enormously fine distinction to distinguish different ways a preposition is used to connect two clauses, then count the number of occurrences to draw a conclusion about its meaning in one particular instance - prepositions are the most notoriously ambiguous and flexible words in any language. This makes it doubly seem ideologically and not exegetically driven." - Dr. Kim Paffenroth, M.T.S., Ph.D
"It's essentially a non-problem. I assume the latter (or substitutes, e.g., heõs hotou) prevails in NT Koine and presumably what is missing in such expressions is a noun like chronou, until such time as . . .. The real issue, as I see it, has nothing to do with the alleged fine distinctions between heõs and heõs hou, but with the verb tenses and/or moods used in the various heõs hou clauses. It is these that may shift the meaning of heõs hou, which is simply (after all) an expansion of heõs which would have been adequate in and of itself in any of these expressions." - Rev. James. P.M. Walsh, S.J., B.D., Ph.L., Ph.D., NAB OT Rev. Comm.
"As in English, the Greek (or any other) word for 'until' (or 'while' or 'as long as') may imply either 'and then it stopped' or 'whether or not it continued after that', depending to some extent on the context. [It depends], inevitably, to some extent on the expectations or convictions of the reader, especially if of profound religious importance. Hence, I would have to give you two warnings: (1) no statistic or tabulation will ever succeed in eliminating completely the innate ambiguity in relation to the reader's Vorverstaendnis or expectations; (2) You must be intensely on guard against being influenced in any conclusions from your statistic which are frankly or subconsciously anticipated or hoped." - Rev. Robert North, S.J., M.A., S.S.D., Editor, Elenchus of Biblica.
"The context of Matthew 1:25 implies the author is interested in asserting the virginal conception of Jesus, not in asserting anything about what happened after his birth." - Fr. Dennis Hamm, S.J., M.A., Ph.L., Ph.D., Professor of Theology, Creighton University
"Heõs is a preposition meaning 'until', 'up to', 'as far as'. Heõs hou is a prepositional phrase. Since the context indicates this phrase is temporal, the usual meaning is 'until which time'. It is my opinion that his phrase DOES NOT relay any information about what happens after the termination of the contextual event (giving birth). It DOES NOT say how long Mary remained a virgin after that event. We only know through other passages that Mary did not remain a virgin for a long time because she had at least 4 other sons and 2 daughters. According to custom, there would be a brief waiting period after Jesus' birth, and one would expect Mary and Joseph to consummate their marriage soon after that; but I believe this phrase does not specify that in any grammatical or syntactical way--it is out of view." - Dennis Hukel, Critical Consultant/Translator, Lockman Foundation.
"In regard to the meaning of heõs hou, there is nothing in this expression itself that explicitly indicates or necessarily implies reversal of action. It simply indicates that something is the case up to a certain point, or 'until' whatever temporal marker is stated following heõs hou. A reversal can be involved, such as in Mt. 17:9 or Mt. 18:34. But heõs hou can also be used to indicate action up to a point of completion, as in Mt. 13:33, or something done by some 'until' others can join in, as in Mt. 14:22, or even something done by some 'while' others do something else, as in Mt. 26:36. In Mt. 1:25, heõs hou is properly translated 'until' because the dependent verb tikto refers to a specific momentary event that marks the end point of the time period under consideration. Joseph refrained from 'knowing' Mary up to the point of her giving birth. What happened after that point is not explicitly addressed in this passage. Nor would I say that what happened afterwards is in any way obviously implied. Rather, the author simply is not concerned with it. He only wants to maintain that there was no sexual intercourse prior to the birth of Jesus, because his concern is solely with addressing questions about Jesus' parentage. Whether or not Joseph and Mary had sexual relations after the birth of Jesus is beyond the scope of interest for the author, and in fact is never addressed in the New Testament. Any argument or claim about this issue is necessarily speculative. We simply do not have the information to state anything conclusively about it.
On this question of the distinction in meaning between heõs hou and heõs alone, we can only talk about tendencies of meaning, not any hard and fast distinction. Heõs alone tends to be used more often for indefinite expressions of time, up to, including, and through the event mentioned following heõs. Heõs hou tends to be used more often of expressions of time up to a specific point, and not including or through that point. But, having said that, we can see examples of heõs used alone that has that same latter function ('until'), as in Mt. 2:15, Mt. 11:13, Mt. 24:39, Mt. 26:29. We even have a case where, in the same passage, heõs hou is used interchangeably with heõs (Mt. 18:30, 34). Heõs hou is sometimes used with the looser meaning 'while' or 'in the meantime' (Mt. 14:22, Mt. 26:36). So the particle hou does not, in itself, determine the meaning of the expression heõs hou. The larger context of the expression heõs hou has that determining function. The expression had a range of usage, and while the inclusion of hou tends towards more specificity of a point of time (as the literal translation 'until when' suggests), it does not always or necessarily have that meaning." - Dr. Jason Beduhn, M.A., Ph.D., Associate Professor Biblical Studies, Northern Arizona University.
"I'm writing a commentary on the Testament of Abraham and looking at all the textual variants regularly. It's absolutely amazing how many times someone thinks a noun should be dative, someone else accusative, how often someone changes a verb ending, etc. The scribes are constantly changing and correcting the grammar of other scribes; that is, these native Greek speakers aren't all following the same rules; what sounds best to one doesnt sound best to the other. No one was reading Blass Debrunner Funk. It's no different today. Some writers think you can now use a plural verb with a singular noun; others of us think this terrible. Some never end with an infinitive, others dont care. The rules are artificial secondary constructs that describe, but always imperfectly. Language is always flexible." - Dr. Dale C. Allison, Past Editor, Journal of Biblical Literature.