It is surprising how easy that can happen. I returned to a client to help with the next generation of a product they were developing. I helpwd with the S/W for

It is surprising how easy that can happen. I returned to a client to help with the next generation of a product they were developing. I helpwd with the S/W for the earlier generation. The people working on it when I returned had the source code but none of the supporting documentation. The documentation wasn't extensive and without my help, it might have been difficult to understand anyway. (Or maybe I underestimate the folks working on it at the time.) The bigger problem was that they had no idea what was missing, let alone where to find it. Much of it included descriptions of why things were done the way they were. On my return, I knew what was missing but had no idea where it was. In the ensuing decade, the company had been through three generations of documentation archives and I had to ask to get access to anything in the new system. I didn't know what to ask for. Further, they gave me a new login and could not provide access to my old email account. (Much of the documentation was shared via email attachments.) I got lucky and ran across another engineer who had worked on the project and had saved a bunch of stuff. He was now with IT, had helped with the document migration and knew where I could find it. I found that a pretty tenuous way to propogate technical history. That was over a ten year period and many of the participants were still alive and working there. Any break in the chain and they would have had to start the next generation from existing code and the embedded comments (which would be cryptic if you didn't understand how and why the system worked the way it did.)