Depends on the situation. If a player is digging up their NES, then yeah, they should expect to look up outside info or the manual. But if a publisher is releasing an emulated retro collection, they should be the ones to provide the manual and highlight its availability.

That’s a really good point— I wish retro collections did that more. (That said, that’s a problem to level at the current distributor of the software, not the game itself.)