I'm not sure that is quite right. I think the 400 was considered a different model than the Aristocrat (it certainly had some different features). The "Big B" is an Aristocrat (Big B refers to the bell engraving). Here's how I understand it (very roughly dated in order of models):Carbs said:
1920's: True Tone (split bell keys)
1930: "New Aristocrat" (split bell keys)
1930's - around '45: "Series one" Aristocrat (left side bell keys)
Mid to late '40's: Big B Aristocrat
Late '40's to mid 50's: 156 (tenor)/140 (alto) Aristocrat; identical to Big B except for engraving.
Late '40's to late 50's: 400 "Top Hat & Cane" (bell keys on back of bell)
Late 50's to early 60's: later 400 model without TH&C engraving. Also the bell keys were moved to the side at one point.
I may be a bit off on some of the dates, but that's the right order. Also, the earliest "Big B" Aristocrat tenors had a smaller bell (like the series one 'Crat). The later ones and the 156 had a larger bell.