So is it correct to say that the tradition claims that one ahruf was selected by Uthman?
Yes. The tradition differentiates between the ahruf and the readings. No early Muslim conflated the two.
The early C14's point to an earlier stabilization of the rasm.
Half these datings are wrong.
An interesting paper from a very controversial muslim and muslim website (quaranist I think) on the different readings of the Quran.
What is the gist? He seems to conflate the ahruf and the readings.