That's how I understand the issue too, Abdal Qadir. The seven ahruf can be looked at as variables, which can change. The mutawatir qiraa'aat will each be composed of these 7 ahruf in different ways. Thus, potentially, there could have been more than 10 mutawatir narrations, but that's just how things unfolded in time. All are equally valid since they only vary in terms of those ahruf, but they do this in different ways. So yes, I'd tend to agree with your last statement, unless a knowledgable brother like sayyidi Abu Hasan could correct us. That would bring me on to the next issue: Is it really a requirement that the Messenger of Allah salla Llahu 'alayhi wa alihi wa sallam be heard reciting the entire Qur'an in every single way, exhausting the various possible ways that the ahruf could be changed? Surely that would be impractical, considering how many potential possibilities there could be. As long as the qiraa'aat only varied by the ahruf, they would be valid as per the hadith, no? The fact that people like az-Zayyat were known for mixing the qira'aat narrated from Imam 'Ali and Ibn Mas'ud (which were different, owing to the Quraysh vs. Hudhayl difference) seems to reinforce this idea.