Yes, I agree, but my point was, if it has been exposed for too long it will have already oxidized. Yes, you could still solder it if there are still exposed good bits of copper, but the connection would not be as good as it could be.
Yes, you can clean it, but I still think it's best to start fresh.
Okay, I didn't get your point, because I've never had the problem that a wire was too old (and hence too oxidized) to be soldered. Sounded more like "don't use copper, because it oxidizes", which didn't make no sense at all.
Surely a fresh start is the very best, but I don't know if it really makes that much of a difference.