I haven't hit the bottem yet, but I know I'm out of codes.
If you don't get a PM from me within the next day or so, I'm sorry, but the codes are gone.
As for the codes becoming invalid, I can't help with that. Some people are swearing you can enter 2 codes every 24 hours, while it doesn't seem to work for others.
If the first code you try doesn't work, wait a week before you try entering the second. I can't take the codes back as the system invalidates them and they're useless from that point on.
Good luck to everyone who got a code from me.