I am not in disagreement with you on your point about the possible literary license in Sudhalter's use of the word "latest."
In fact, that's why I went on to say that the next step would be to determine if his notes or recorded interviews suggest or show that McPartland actually mentioned that Bix had a fairly recently purchased Conn Victor--or not. If Jimmy didn't describe Bix's cornet as a relatively new Conn or use the words "new" or "latest," or similarly terms, we'll have to assume those were Sudhalter's words only.
Even so, Bix could have bought a new cornet from another musician and left no paper trail for the purchase. We don't know quite everything he did, after all.