There's a way to have them tested now, but for a really long time there really wasn't (not publicly and for free). A few people had EPROM progammers, and that was it. Now I've got an EPROM emu, you've got one, and more people at least have NROM test carts.

I definitely agree though that there does need to be a working/not working classification. It's good to know, because it's pretty tough to program for a system when you don't even have one. Many of the broken ones are probably easily fixable too, but we know how it is with updating years-old spagetti code, heheh. And once they make it into the GoodNES database or whatever, they're irretrievably out there.