They're not 'all the same' That is; the catalog you're showing of 9552 and 9553 A are the same 'fit'. However, these would also fit Schwinn's middleweights, post 1955 or so b/c the top and bottom tubes are the same distance. But, a big butt as in butt head. Schwinn excluded the cross bar in later middleweights, moved the rear bracket back about 3/8" with a little twist. That rear bracket smacks right into the cross bar of earlier models so, you can not mount it on earlier frames. .
I think you'll be safe with the DX feather, 9552A Yet you'd think this starlet tank with embossed lines would tell? :
but, beware; the newer version should have an extra bracket off the rear bracket with a screw to chinch down into the bottom bar but, I can no guarantee it's a sure tell. . Both nearer and older come in all flavors chrome, embossed, 3 gill 4 gill, flat standard, one color 2 color etc. . This example,
below, is the newer and has the extra tab to chinch it into the bottom bar.
However! Other than that, it's identical to the Starlet tank above except, it's chrome,
2nd photo below. .
PLUS they come in chrome and painted too. The major difference is not just the added cinching bracket, the rear bracket has an slight twist, changed angle, and there is absolutely no way, without removing, repositioning and welding it back on to fit earlier girl's frames with the cross bar.
Inside
Outside: