Each file represents a module in our business management software (e.g. documents/contacts/memberships/events/etc). Historically, we have replace entire modules

Each file represents a module in our business management software (e.g. documents/contacts/memberships/events/etc). Historically, we have replace entire modules with ones that fulfill new/improved/different needs. For example, we have a module called "membership 3", because as we have obtained new clients, "membership" and "membership 2" just were not structured to do the things the new clients needed. When the company started, we were full of inexperienced devs with no official programming education/experience. Now we have a team that is more aware of things like design patterns. As such, the newer modules are easier to extend and add new features to, so we anticipate that rewriting entire modules should not be necessary when the newer versions need new features. So to answer your questions, we are just waiting for the old versions to die, and for somebody to pay enough for a job that we can rebuild the old module from scratch :) Of course, contributing factors such as time, blah, blah, man power, etc. come into play also. Always things that need to be done, never the time to do them.