Their Conflict with Consensus
These reports contradict the unanimous belief of all the Muslims that the only way of establishing the authenticity of the Qur'an is tawattur, which means `a continuous and wide spread acknowledgement'. If we believe these reports, then it would follow that the Qur'an is established as authentic by reliance on two witnesses at every stage of compilation, or one witness whose testimony was accepted as equal to two. This means that the authenticity is proved by an isolated report also, a concept unthinkable to a Muslim. I wonder how can we reconcile between the two; one telling us that the Qur'an depends upon evidence, and the other telling us that it had an unbroken, widespread currency among the people ‑ tawattur, needing no further corroboration. If we accept the consensus that the Qur'an is evidenced by tawattur, then we have no alternative but to reject all the reports contradicting it.
Surprisingly enough, Ibn Hajar interprets two witnesses as "written evidence" and "evidence of memorization". I believe he had to take recourse to this interpretation so as to avoid a conflict with the fact that the Qur'an is based on tawattur. But even this interpretation has many faults:
(a) It is contrary to the evident meaning of all the reports you have so far seen.
(b) This would mean that no parts of the Qur'an, however explicitly based on tawattur, would be accepted if they were not written down by someone. It becomes quite probable that certain parts of the Qur'an which, though current and widespread, were omitted because there was no written evidence.
(c) When tawattur exists, the written or memorized evidence is superfluous and redundant. In fact, such evidences would not be acceptable as parts of the Qur'an, if they do not comply with tawattur.
In fact, there is no alternative but to reject all these reports, because they prove the authenticity of the Qur'an on things other than tawattur. And the consensus of the Muslims lends no support either.