Depending on how you paid, your V3 Gold license # should be on file with Ventis, or in a payment receipt, or in the Help About or settings of Mediamonkey (I seem to recall it's displayed). I keep those things on a NAS with escrowed installers and config files, as well as LastPass (which is superb, and a bargain value of $12/year for premium which allows mobile use)(end of shameless plug).
I bought Lifetime when I decided to use MM for my entire digital library. I use maybe 40% of the features, but based on what I saw, made a commitment that I would continue using for several years, faults and all. Since 3.x was in its last year or so, I presumed that I'd be buying a Gold license again, and felt that buying the Lifetime took care of that and then next version after. Ventis and MM have been around a while (I found reviews going back a few years) so I didn't worry about my extra $ going into a company that would die off.
«Tell me and I'll forget; show me and I may remember; involve me and I'll understand.» Chinese proverb
T43 XP-SP3 2GB RAM, dual hard drives, MM 4.0.3 Gold; Ipod Classic 7G v2.0.4, Nano 3G v1.1.3.