I just discovered that my 1968 Buick Service Bulletin binder includes a 1968 Protect-O-Plate order form. On it there are all of the fields for the POP with the title of each section. It only contains the info for the 1968 Build date codes and the Option codes. The engine and transmission codes include the Julian day codes the components were assembled.
Cool! I also have one for my '70 GS. But mine happens to be a copy of a filled replacement POP order form, dated 1971 IIRC! -JJ-