I don't recall which one it was, I think it was 12.7 to 12.8, it was a fair few ago though....
If that's the case, you must had not done the upgrade correctly. I'm guessing you simply extracted the NL.exe file for the newer version into your existing one. Anytime you go from version 12.X to 12.X+1, like from 12.7 to 12.8 as you mentioned or from, say, 12.84 to 12.9, instead of extracting the NL.exe in the same folder as your existing NL directory, you needed to set up the new .exe in a different folder. Then, if you wanted to carry your current progress over to the newer version, all you had to do was copy over your settings/levels folder from the previous version to where you extracted the newer NL version. Similarly, if you're going from say 12.8 to 12.81, it's much easier and you can simply extract the NL.exe on top of your existing one. However, if you ever have doubts, you can always play it safe and make a new folder before extracting the contents of the newer version and then copy over the settings/levels folder.