I have a Perfect Percussion badge bassdrum and racktom, no rerings and painted grey, they all came with Star hardware though, and sharktooth lugs. Probably was a Royal Star. I have a similar Royal Star tom (tonneau badge) that I converted into a lamp that has the exact interior and lugs.

Latzanimal: my thin rering Imperialstar bass drum has a thinner shell compared to my thick rering Imperialstar bass drum, almost 1 mm difference. Measured from the bassdrum tom mount hole.

But it's all possible.

1 mm difference could mean nothing more than one thicker ply... tolerances back then were much more relaxed...

If it's 1 ply less, would mean saving some money on shell construction. But who knows. Both basses sound good. I don't have the same heads on them to compare them though. But I dont think that 2 24" bassdrums would sound so much different with less than 1 mm difference