In which case we honestly have no idea which text is reliable and therefore it would be dishonest to take either (in part or in full) as "gospel".
First, this argument might be valid if the gospels were chosen upon historical evidence. But the gospels were chosen because God and Church revealed the gospels. And because all of the NT authors quote from the Septugaint, the Septuagint is a worthy translation, if not more worthy than the Masoretic that developed by Jewish tradition. The Septuagint, of course, could have some errors but no error that would disqualify itself from canonical Scripture.
Second, it betrays a misunderstanding of the weight of Scripture. While all Scripture is good for reproof and correction, Scripture is to be interpreted--not by men but by God revealing Himself. Hence the Scriptures can have imperfections as long as God's revelation to man is correct.
But if the Scriptures have imperfections, then it begs the question of why God allows these small imperfections? Well, it's possible that God allows small errors so that men, even when reading the Scripture, go to Him for their questions. Why should men go to their own contorted understanding of particular passages? If the Scripture came in perfect gold, written in stone, written to be perfect, then we would still have the law written in stone.
Now back to your second point. If I say, "the Bible says Christ was crucified," then the statement is true: that is what the Bible says. On the other hand, if I say, "Christ was crucified," then the statement is false if Christ was not crucified. How does this apply to the case mentioned? Well, if you read relevant portion of the Bible concerning the prophets raising from their graves, only the reports were mentioned. Whether whether the reports were false or not was not mentioned, and so we believe these reports were made by trustworthy individuals.
This idea that the reports are trustworthy is further developed by there being little reason to reject the reports.
The occurrence and site of prophets is not a new thing: Both Peter and John saw Jesus speak to Moses and Elijah, not in bodily form but in spiritual form. Hence the prophets, so also, must be in heaven, not in bodily form but in spirtual. Of course, this view may contradict the doctrine believed by some Christians; it does not, I believe, contradict the Church's.
Furthermore, there are visions of saints such as Ignatius, who is seen in heaven, and Stephen, for whom the sky opened; the doctrine of the spirits of the dead going to heaven is an early Christian doctrine and is recorded in the Bible. Although the book Ecclestiastics suggests the dead know nothing, remaining in the ground, this depection was a poetic Old Testament view of death: Why accept this book's depiction after Christ's death?