Is it possible they confused a decision about the end title arrangement with the main title? There seems to be several variations on that as well.
No, the end title variations correspond to the main title ones -- after all, it would've made sense to record them in the same sessions.
Solow repeats this story about dropping the soprano version in his Archive of American Television interview (from 2008).
Sometimes people forget the order in which two things happened. A while back I saw an interview with Leonard Nimoy from a few years ago in which he talked about his time on Mission: Impossible
, and one of the numerous factual errors in his recollections was his claim that Lesley Ann Warren was his co-star in the first of the two seasons he did, when in fact it was the second. Given the choice between an oral account decades after the fact and documentation from the time, you go for the documentation. The people who put together the soundtrack box set had access to the original master tapes, sheet music, documentation, and written records -- that's about as primary a source as it's possible to get. Solow just seems to have been going from memory. There were other claims in the book that he backed up with documents and records from the time, but this doesn't seem to have been one of them. The box set's ordering of the title cues is based on primary documents, so it's the more reliable source.