Sorry, I'm not making myself clear. Let me try again. The issue is not whether Isaiah precludes the possibility the Messiah would be born of a virgin, the issue is that Matthew SAYS scripture explicitly states he would be born of a virgin. The Palestinian canon, it is my understanding, DOES NOT explicitly state the Messiah will be born of a virgin. Hence, given the Protestant canon derives from the Palestinian canon, there is a descrepency between what Matthew SAYS scripture says, and what that scripture actually says.
In other words, if I were a good Berean and brought to my reading of Matthew the same sort of empirical literalism as some in our day and age bring to the reading of Scripture, it seems to me my first reaction would be to demand of Matthew, "Scripture, please," and then accuse him of adding to scripture.
I agree. But, as I would point out, this is not the only such discrepancy.
Obviously, the author of Matthew held that the Septuagint was an inspired translation -- sort of the way KJV-only believers think that the KJV is more inspired than the original-language texts.