I'm talking about internal libraries of a company, where there is no proven library with a stable interface as it's continuously evolving - similar to a young l

I'm talking about internal libraries of a company, where there is no proven library with a stable interface as it's continuously evolving - similar to a young library in the OSS world that has no reasonable substitute. It might be something like a new parameter to a function, or an additional method call you need to make in a given version.