The SDS9 bassdrum pads have a thin plastic frame which is screwed through the bowl to the wooden board. If you loose these screws, both board and bowl will come off. If you have an SDS8 pad, you don't have this frame. You only have the rubber surface which is wrapped and glued around the bowl while the bowl itself is stapeled to the board.
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> I also found a "inspected by" sticker inside that has several numbers
> that indicate it might have been manufactured in November 1985 (the
> numbers were something like "261185")
>
in 1985 it could be both: SDS8 or SDS9 :-)