"willfull" vs "innocent" infringement can carry different weights.
Same on the owner's side. If you didn't know someone was using your IP, then you didn't know, and that won't take away your rights, but if you did know and ignored it, you could be seen as having silently accepted the infringement. But you don't LOSE your copyright. That would be silly.
Trademarks are a different story. Its pretty well known that if you dont defend it, you can lose your claim to it, since the purpose of trademarks is for active use in commerce, and they don't want companies tying up any and every trademark they feel like (it's not like registering domain names).
Back to copyright, you could do all the due diligence and keep a paper trail proving you could not find a copyright's owner despite thorough searching, and then proceed with its use, and then later if sued, damages could be negated (as "innocent" infringement rather than "willful" infringement). Even if you are not penalized with fines, you'd still have to settle with the claimant for their fair value licensing costs, and if you didn't put money aside for that, it could still hurt.
I was already under the assumption that Ultracade's use of Universal games was under just that premise, since nobody seemed to have any idea what happened to Universal games. I guess now we know who owns them.
