And I'm out of my depth arguing with you. I have a weak mind, and the first time I heard of this piece as a possible Bix item, I think through this forum, I WAS swayed into thinking it was Bix, though not 100%. I recall thinking the note was an interesting choice (though I didn't notice until you pointed it out that he holds it for the entire 4(?) beats after the chord change to A7). But I think I thought that maybe Bix ran out of energy. All other aspects of the solo seemed to be Bixian to me, and it seemed clear to me that whoever played this solo was NOT the person who was playing the lead. And, as I am not a professional musician and spend at least as much time listening to classical music and to more recent jazz as I do to 1920s dance music, the note didn't/doesn't seem "wrong" to me at all.
Thank you so much for your analysis. I thrive on the kind of detail you offered, and at the risk of alienating you, I have several comments, perhaps questions.
First, you hinted that further evidence that it isn't Bix rests in the phrasing and articulation. Will you elaborate? Because I don't hear that at all. To me (untrained!), the phrasing sounds like Bix.
Second, I am convinced that Bix, somewhere, has played just this type of 4th before. I have been wrong in the past, heaven knows, but now I need to dive into the records, sit at my piano, and prove it. This could take months! If I ever come up with an answer, I'll post my findings.
Third, and I'm really out of my depth cause I've never focused on Margulis at all, but have heard a lot of Secrest through listening to Bix. To me the lead has the one huge thing I always associate with Secrest, the doubling-up and playing the same note twice quickly in succession in a solo. I'll go out on a limb and say I can't recall Bix doing that. Also, the tone the lead gets, which is more of a brassy sound than Bix played, sounds like Secrest. I don't know about Margulis.
Fourth, can you please deal with "Waiting at the End of the Road" when you've got the time?