In regards to your software development comparison, that happens all the time. Someone decides, this system is already so complicated it would be a mistake to try to bake in all this additional complexity. A more sensical solution would be to design a different system for handling these or deal with them in one-off cases if they are infrequent enough.

Vague metaphors aside, this happens occasionally in the industry I'm in (finance) when we trade small lots of non-traditional products. These products don't follow many of the rules that all of our other traded products do. Instead of re-writing our systems to deal with these(totally impractical), we manually shimmy these in to the database until they expire or are traded away, at which point we can forget about them.