[makecheck]

Robust scripts require diligence appropriate for the environment. If you’ve deployed systems with different default tool versions, you factor this in, e.g. by installing a common version that both can use (or just make scripts that can figure out how to work either way). Two versions of a tool isn’t really any different than two versions of a compiled-in API, except that APIs tend to be more rigid (not always, e.g. some languages allow runtime querying).

There’s a common rule in Unix-like systems that essentially says “inputs are liberal, outputs are conservative”. It matters to have programs that can adapt, because this makes a lot of things more practical.