(Pete) Here's the reasoning on this section:
There's definitely a Modele 28 out there. I have a few pics of one in the gallery.
There's a New Largebore (NLB) model. I have an album full of pics of those.
... And there's something else ...

I started to get a bit confused looking at some 1928 and 1929 horns and comparing them to the NLB: they have, at least, a different G#/C#/B/Bb cluster than the 26 or NLB.
Some have a G# trill, altissimo D# trill, and/or a fork Eb keywork, so I don't think it's right to call them NLBs.
"Transitional" is about the best compromise.

I've also noticed that the soprano goes back and forth between the Modele 26 design and this "Modele 28 Transitional" style, which is both annoying and interesting.

I created a sortable and searchable lists of about 75 altos and tenors, from the Modele 28 through the Jimmy Dorsey and Selmer Super Series horns.
I also wrote some commentary about these horns on the Woodwind Forum. Check it out!

Model 28
Model 28 Transitional