ITunes displaying wrong thumbnails for locally stored music on Windows
I've only ever used iTunes as a convenient way to organize and play the rather obscure music I have downloaded as mp3s on my computer. [Note to mods: this is not a piracy post - these are audios I took myself] I used to have a MacBook, and on it, I'd strip metadata from the files, open them in iTunes, and then use song info > artwork to upload thumbnails. To save space on my computer, I wouldn't keep the original thumbnail images once I uploaded them.
A few months ago, I switched from a mac to a windows machine (technical details below). To my surprise when I downloaded and opened iTunes on my new laptop, tons of songs in my playlists were all displaying one thumbnail, that of the alphabetically first song on the recently added playlist. The correct thumbnails still show up if I look under song info > artwork and in that little bar on the top of the app if I play one of the songs affected.
After some digging, I found out that the reason seems to be that Windows iTunes automatically lumped most of the files I had cleared metadata from (most of the oldest were spared, but there seems to be no consistent pattern) into one giant album called 'Unknown Album' 'Unknown Artist.' I found that manually going into the song info of one of the affected songs and adding a dummy album name fixed the problem, but only on that one individual song. I also tried adding a dummy album to the alphabetically first song on the recently added playlist, but all that did was lead to all the songs affected changing to display on playlists the thumbnail of the alphabetically second song on the recently added playlist.
Is there any faster way to fix this as opposed to going through 1500 songs and adding dummy albums one by one?
Device (and Model): HP Envy x360 2-in-1 Laptop
OS Version (If Applicable): Windows 11 Home 23H2
App Version (if Android/Windows or if applicable): 12.13.2.3
Region: N. America
Steps you have taken to fix on your own first: See above