OK, the most useful resourceful reference then (aside from the manual) would be enough gameplay footage. That makes sense. It's nice that these two videos you posted cover the majority of the game. However, I'm guessing most of the remaining useful gameplay footage would involve trying all sorts of things in the different levels/menus. For example: What happens if you don't jump over this ledge? What happens if you die to this boss? Do boss attack patterns have any consistent pattern to them (or is it all random)? What do those password codes do? What do all the menus look like? All that sort of stuff that doesn't typically all happen within one single playthrough of the game unless you had these things in mind while playing.
One other thing that might prove an issue is that in every video I can find, the footage doesn't show what buttons are being pressed. So without another reference, I feel like a lot of guesswork would be needed.