If these reports on the collection of the Qur'an were accepted as true, then an argument suggesting some possible omissions becomes plausible, and together with it, one has to concede that some additions also ‑nay have occurred. The way the process of compilation has been described justifies such a presumption.
It may be argued that the eloquence and style of the Qur'an prevented any addition without being traced. Perhaps a complete Surah, if fabricated, could be detected, but an addition of a word or two, or even a short verse, would certainly be very difficult to distinguish. Had this been the case, the preceding reports would not have mentioned the provision of testimony by two witnesses. In fact, whenever a person came with an ayah, the very act presented a possibility that it either was from the Qur'an, or it was not. Thus we are faced with an ever attending curse of interpolation, while the consensus of Muslims is that the Qur'an is intact from all tampering and profanities.
To summarize, we say that to attribute the collection of the Qur'an to the Caliphs is based on mere conjecture, and it contradicts the holy Book itself, the Sunnah, the consensus and the reason. And therefore, those who believe that the Qur'an has been tampered with or interpolated do not have any solid grounds if they rely on the reports. And if at all we accept that Abu Bakr compiled it during his caliphate, there is no doubt that the process of collection as described in these reports is untrue. The fact is that the collection of the Qur'an was entirely based on tawattur among the Muslims. At the most, what Abu Bakr might have done was to collate a codex or a volume (mushaf) contents of which had already been preserved by the way of tawattur.
Yes, there is no doubt that Uthman produced a copy of the Qur'an in his days, but this was not to say that he collected the verses and the chapters into a book form. Actually, he effected a consensus on recitation according to a single master copy, ordering Muslims to burn out all other copies which varied from his copy. He actually wrote to all towns and cities, forbidding Muslims from entertaining different recitations. This has been substantiated by many Sunni scholars.
Al‑Harith al Muhtasibi says: "It is commonly held by the Muslims that Uthman was compiler of the Qur'an. This is not so. Actually, Uthman enjoined upon Muslims to unite on one recitation, acting on the advice of certain Muhajirin and Ansar who feared disunity resulting from some confusion among the people of Iraq and Syria in respect of recitations. Before that, there were various copies having recitations based on the "seven readings" upon which the Qur'an was revealed ...."1
I say that Uthman united the Muslims upon one mode of recitation, the recitation which was already current and known among the Muslims, the one which they had heard from the Prophet (‘s). He forbade all other systems which had developed based on the so called report about the Qur'an having been revealed according to "seven readings", and I have already proved that this report is untrue. Uthman was never censured for this, because the different recitations were bound to bring about disunity and discord among the Muslims. In fact, each group had begun to label the others as infidels. And the Prophet (‘s) himself had forbidden any differences in respect of the Qur'an. However, Uthman was censured for having burnt up the rest of the copies of the Qur'an, and for having ordered the Muslims to do so. A group of Muslims became his severe critics, labelling him as "the burner of Qur'an".
1. al Itqan, v1, p.103