Well, that's half a step into the right direction. But if a (security) update modifies the version in lib, the admin might want to merge the change with her/his own modifications. But who tells when such a merge might be needed?
Myself I like etckeeper (with git) for that purpose. Works perfectly with SysV init scripts (and of course everything else under /etc). Unfortunately it would no longer identify lost update situations with systemd's half solution. Maybe use the right exisiting tool for the purpose, instead of trying to solve a problem of versioning once more. Admittedly git is not 100% the right tool for /etc, but close enough.