CS4 - License suddenly invalid and registered products gone from Adobe acc?

Background: I got Master Collection CS4 from an education/academic reseller around 2011, installed it on my Vista laptop and registered it, and had no problems with it at all. When I replaced the laptop earlier this year with a Windows 10 system, I checked my Adobe account for the serial numbers for CS4 and Acrobat 9, downloaded the installation files and installed and activated without no problems. I've used several programs in the suite since and everything worked as it always has.

A week or so ago, Win10 installed a major update, and the next day when I tried to start Photoshop, instead the licensing/activation screen came up, asking for either a serial number or to start a 30 day trial. When I re-entered the original serial, it was reported invalid. I looked on the forums and it seemed to be a common problem, particularly after updates, so I started following one solution Error: "Licensing for this product has expired" | Adobe Creative Suite 5, Adobe Creative Suite 4 (reset the system clock to Jan 1 2006 in the hope that I could start the software, deactivate the license, and then re-enter it), but Photoshop just put up the activation dialog instead. I ran the LicensingTool (Error: "Licensing has stopped working" | Windows ) and followed the instructions (which I understood can repair/refresh the database files or then clear the license if that doesn't work), but no change. I was then going to move on to the next solution, but decided to check my Adobe account just to make sure I had the serial correct - I found that both of my registered products had disappeared from the account. When I tested registering the serials, the CS4 one again said it was invalid and the Acrobat one said it was already registered (by me originally, I assume?).

I wasn't too concerned (as there's plenty of troubleshooting advice like the above for corrupted installations etc.) until this point, but it makes no sense that the registered product info was erased, no matter what problems the software on my machine has. I contacted chat support, and the agent confirmed the license was invalid - they also checked my alternate email just in case an Adobe ID had been created for it and the registered products had ended up there, but that wasn't the case and there was nothing more they could do. In the end, I have what should be a working copy of CS4 with a suddenly invalid license and no evidence that I even registered it (and I don't think my original receipt for CS4 came with me when I moved to a new country)!

Is there anything that can be done? I heard that Adobe might be cancelling some types of previously issued licenses for CS4-6 - is that why the license is suddenly invalid and the registered product information vanished from my account?