The sticker labels was used for a short period during late 81-early 82. The Boss Book lists the Roland Japan label as a label used on the earliest Boss pedals. Now and then a pedal with this label pops up on Ebay but they always have a black thumb screw so the theory about it being used on the earliest pedals breaks. After your discovery it looks like the Roland Japan labels were never really used without the sticker. In some cases the sticker may have fallen off or been removed and we (and the authors of the Boss Book) thought it was a new label.
The CE-2 was produced all the way up until the early 90s so the information about end of production in 1982 is incorrect. Most likely Boss planned to write 1992 but wrote 1982 instead.
Yes I have seen this label, it is kind of a rare thing where the black label was printed "wrong". it said "roland japan" and like bossarea says above, the sticker was used to clearly designate location of manufacture which is very important for import export duty/tax purposes. I would think that the pedals that have the sticker in tact would be "more" collectible than ones that don't because it was a band-aid solution to a production printing error. Maybe i'm full of bull, but you DO see these around. I had a very very nice BF-2 with one of these labels on it and it swoooooshed withgreat authority