Recurring damaged itunes library and no way to reimport already downloaded media

Hi, I've used iTunes on Windows for over a decade, and in the last 2 years, I've begun to encounter random damaged itunes libraries every 6-12 months since. There's no pattern behind when the library decides it's damaged, and it has 0 impact on the same library on apple music in my phone. However, when restoring the iTunes library (either from iCloud or from a backup .itl file), there's zero option to match existing downloaded files with existing content in my iCould Library. As someone with an extensive CD collection, this means I either need to delete and reupload all 1500+ albums in my library, or I need to take up 25% of my monthly data cap to re-download files that are already on my computer to allow them to play in iTunes. This is made so much worse by iTunes refusing to download any Apple Music content over my ethernet connection, so I'm forced to use Wi-Fi that's ~10x slower.

Does anyone have any insights into how to avoid this broken library in future (or has any idea why it would suddenly start occurring after 8 years of use), or how I could get iTunes to match existing files on my computer with files in my iClould Library?? It's so frustrating when this happens, and it really undermines everything I enjoy about using Apple Music and iTunes.

Thanks in advance