It doesn't matter how you store your maps or where you store them, as long as you make sure that the place you copied them to contains the same data. Other criteria are: how much data do you have and how long are you planning to keep it?
As for the backup itself: you should have verified the content of the DVD before wiping your disk. Most (if not all) CD/DVD burning applications come with data verification. It may take some additional time, but it's the only way to make sure that your files haven't been corrupted during the process.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.