Second, regardless of when Severian-the-character becomes threefold, Severian-the-writer is threefold all along. Now, presumably, he can perfectly recall being just one person, or just two, but other evidence suggests that he doesn't have perfect control of his personae. Is there a point at which the old Autarch asserts himself?
This is one thing that's always bugged me a bit about New Sun. In Castle of Days, Wolfe mentions (as I recall...please correct me if I'm wrong) that certain things about book 4 came as a bit of a surprise to him. I've always wondered if the Autarch mind-meld was one of them. If it was, it certainly casts some doubt on how much we read in to the Old Autarch's presence in the earlier volumes. That bothers me because so much of our reactions to small hints in the early volumes depends on assuming that Wofle had the full story in view the whole time. But it does make me stop at times when I start to try to put together ingenious readings of Sev's perfect memory combined with Thecla/Autarchs...at least in the early volumes.