A2S4000 was the original IIc case and was used with the Rom 255 and ROM 0 motherboard.
A2S4100 designated the ROM 3 and ROM 4 motherboard.
At some point the case had some slight modifications. The rear case panel was removable on the original IIc’s, it then became one piece with the top case (see last photos). The lower shield was removed and the inside of the case was coated with black (pretty sure this one is a A2S4100 change).
Lower case assy comes with feet, speaker, and shield* (the cases with black inside never had that shield)
Upper case assy comes with back panel* (later cases were all one unit), screw clips for the handle, light pipe and Apple emblem.
Complete case includes matching upper and lower cases. All are interchangeable. Expect minor scuff and scratches as these are 35 years old.
A) Upper Case (2 pc early) Medium to severe discoloration (far right in photo)
B) Complete Case (early) Nice to light discoloration (main photo is this case) OR it’s parts below. This one has minor pry marks from someone trying to figure out how to open the case.
C) Upper Case (2 pc early)
D) Bottom Case w/shield (A2S4000)
E) Complete Case (late) Light to medium discoloration (the remaining case in photos) OR it’s parts below
F) Upper Case (1pc late)
G) Bottom Case no shield (A2S4100)