Figured it out!
Ok, came back to post this in case anyone else was having this issue. I should have figured it out sooner, but you know how that goes.
In order to have the same files at home and at work (for instance) after you've done things like deleted some files you don't like anymore, or done a star rating on others, is you have to RESCAN the directory where you store your music.
I keep mine on OneDrive, and now when I go home or go to work, I just press the Insert key to bring up the re-scan/add files dialog.
Make sure to check the boxes next to "remove dead links" and "re-scan files already in the library".
This will update everything, including ratings you've made.