Not caused us any yet over 3 years. You've got to think of it as the opposite, when we find a missing method because we at some point updated a library, we update the ts definition.

So it's not that it's a source of errors as most libraries are backwards compatible.

> Is it not a problem in practice when TS type declarations and their associated JS code are written by different people at different times for different versions of a library?

It can be. But most popular libraries have very good version syncing, or even include definitions in the module itself. In the worst case, or if there are no typings available at all, you can just import the plain js, and use it untyped, which can be acceptable if it is not used in a lot of places.

> didn't seem to have any formal reference to a specific version

Yeah. It mostly works if you install the latest version of them both at the same time. Sometimes I've had to fiddle with backing the definition or the module back a version to get them to match.