My local game rental store (rural independent shop, often kept photocopies of the original manual in the case that the game cartridge came in. I always assumed it was because the original manuals weren't going to put up with abuse for long.

Some of the cases had it taped to the inside. But generally we didn't even look at that ... we just figured it out as we went along.

It's interesting that Blockbuster felt strongly enough that they had to put out the manual, when I suspect most kids wouldn't care.