[z1mm32m4n]

I recently learned that a system like this is already described by Haskell’s Package Version Policy[1]. They call the vanity digit the “epoch”[2]. Basically the way the formalize it is that the first two components specify the major component, and a breaking change must correspond to an increment where the new major version is lexicographically greater than before. Depending on the whim of the maintainer this can be by incrementing the first or second number.

[1] https://pvp.haskell.org [2] https://pvp.haskell.org/faq/#semver