not sure if this helps, if you require more, I can contact a mod, but this is an email from vbulletin staff stating my license is available, I will work on contacting a mod right now. http://i52.tinypic.com/2lkplzp.png
Your PM box is full. Anyways, to answer your question, you can only do a transfer once per license, vBulletin only allows it once. So once it's been transferred it can't be transferred again. But since you flip sites, you could just give the person the login details as none of your personal info is viewable and they will always be able to get updates still.
Its better to just verify it yourself, no need to waste the times of the mods. Just give him your customer number, full name and email and he can email vbulletin and find out in less then a couple hours.