Of course, it is always good to have an archive of every software that you have downloaded and installed together with their licensing keys. They is no real substitute for this protocol. 

However, My VMware has the licenses that you have bought, with their serial keys and you can look from there. I have never noticed anything else than the number of computers that one license key is meant for, not necessary it is only one. Thus you can do whatever you wish when you don't exceed the number of licenses that you have bought.

As others here have stated, I'm not a VMware employee, but I cannot see any reason for a more official answer.