Sentinel, as already noted, does not retain copies of the "previous" firmware files.I called UNIDEN Support and it seems it's the first they heard of this problem. Everyone call @ 1-800-297-1023. I recommended Sentinel be enabled to retain previous version of firmware in case this happens again. I borrowed "$700 brick" and it seemed effective. The lady said she would escalate immediately. I recommended redistributing earlier version firmware to Sentinel for an immediate fix. She wrote it all down. We need more complaints!
However, copies of the most recent firmware update are stored on your PC. Before doing an update, I copy those files to a separate folder. After I then do the firmware update, the copies of what was just installed replaces the ones that were there before the update process.mThis way, I have both the most recent, and previous files saved, if I need to roll back the firmware version.
These are stored in a location in the ProgramData folder.