I just took another close look at the files on my system. Yesterday morning I installed MacOS 10.13.3 release version, updated one app and re-installed a previously removed app in the afternoon, and updated to MacOS 10.13.4 PublicBeta 1 in the late afternoon. A thorough search of updatejournal.plist using BBEdit found the two apps I had installed but no mention of either MacOS 10.13.3 or 10.13.4. In fact the the only MacOS release mentioned in updatejournal.plist was MacOS 10.12.6.
The closest entries to "System" apps were Xcode and Safari Technology Preview.
App Store
Updates shows both the MacOS 13.3.3 and 13.3.4 updates and the updated app but not the re-installed app which is consistent with the Updates title. App Store
Purchased shows both the updated and reinstalled apps, but none of the OS updates or upgrades, also consistent since the OS updates/upgrades are technically not
purchased.
I have no idea where App Store is getting its information about the OS updates, but it is apparently NOT ~/Library/Application Support/App Store/updatejournal.plist at least on my system. I checked my wife's system and my server and the results in both cases confirm what I am seeing on my Mac. At this point I can only speculate App Store has another database hidden somewhere in the system or online or maybe it is checking the /System/Library/Receipts folder.
