No worries - the bucket option for that era of RRs is kind of a curveball, as is the dash.
Base car interiors are like Belvederes, Decor Group cars are like Satellites, but with the Belvedere-level dash.
Bucket RRs still had the Satellite door & quarter trim & Belvedere-style dash.
That's my reasoning on the P vs M codes.
4-speed carpet color is likely another P item; that debate should be coming along shortly