Considering that #620 is elaborately engraved, not to mentioned engraved with Bix's name and the date, it's entirely possible, even likely, in my opinion, that the horn was meant to be a keepsake of sorts, and that could explain the condition it is in, (if it was never restored). No one is saying that he didn't play the Bach Stardivarius, just that ultimately, Bix was using another horn more often, from the evidence seen. Just because Jimmy McPartland says the Bach was the best horn Bix had, doesn't mean that was BIX'S opinion. It was most likely Jimmy's, and even if it was Bix's opinion, at the time he got the horn, it doesn't mean it stayed that way, in his mind. Unless we find a journal, or a letter that he wrote, stating it, we'll never know for sure. While the #616 Bach is missing, indicating that, possibly, it was heavily used, there are at least three Conn Victors missing as well. Where are they? Frank Trumbauer, apparently stated that the Herbert Clarke Holton was a horn Bix was very proud of, as well. Where is it? And like Malcolm, Scott Black is of the opinion that in the Fox News Reel footage, Bix is playing the Holton. He has a reel of the film, and has been able to project it on the wall. He says the footage looks considerably better, than what we see on the dvd, and to him, the horn could be nothing other than the Holton.
Since Scott is supposed to give a talk, at the Davenport Bix Fest, it might be a good opportunity to ask him about it, when he takes questions.