I'm in the process of drafting a letter to the Rep from my district about the nightmare that this process has been. I know its not going to change any overarching policy, but I'd at least like for the USCIS to keep the documentation I've already provided for my current visa on file so that I don't need to send them paperwork they've already seen for my first three applications.
Unfortunately, I suspect that somewhere at the heart of the USCIS system an entity relationship is enforced such that there is a one to one relationship between candidates and cases/visas and, thus, no interchange of information between one case/visa and the next. One advantage of this is that there is not likely to be much carryover of any errors between cases. This is purely speculation though.
A better model might result in a one to many relationship between candidates and cases/visas, where only one can be active at a time. This might result in an easier way for the immigration service to query each visa and tell me exactly what documentation is necessary for a transfer. However, this would also involve me trusting USCIS to actually manage and keep my data safe and secure. It would also involve me trusting them not to make any errors when inputting data to their system and for there to be an easy way to correct their data when they do make a mistake.
The one unfortunate thing that I'm sure about regarding immigration issues is that things are not going to change anytime soon. The lawyers who assemble and file visa applications at a very high cost for companies are not going to be happy if the system is made accessible for people to do by themselves. They, unfortunately, have a vested interest in keeping things as complicated as possible.
As for me, I'm going to do the same thing I've done with all my visa applications, I'm going to assemble everything associated with the application into one place (all paperwork, forms, emails, communications etc) and make a digital copy which will be encrypted and stored on a backup drive as well as a physical copy which will sit in my personal safe. Then, I'm going to start my new job and forget everything about the process and hope that I don't have to go through it again for a long time.
Good luck with everything!