I currently have a similar situation in respect to transfering an application from one server to another. The client says X doesn't work and we go back to the old server and lo and behold X never worked.

Now your account handlers have to earn their money by explaining X never worked. Even more fun when the client has already paid for X and been told it was working.

Transfer of applications from one company to another or one group of developers to another is never fun.

UnderMine