While it would not be easy to track a version number, could you add a last Build date for the Plug-ins on Labs, so one is sure of the one that downloaded is indeed the latest or not. In some cases it is just code, in some cases binaries, but unclear on when it was last updated.
Comments
maybe it could be a good idea, to transform labs into a private repository for premium members.
Need to think about it and check out the options