metadata not updating on device even after deleting and reuploading!!

i'll post this on both calibre's and koreader's subreddit coz idk where I belongs.
device: 7th gen kindle PW
KOReader installed
metadata edited through Calibre
sent to device by copy-pasting epub file into kindle folder through USB

ok so, here's what's going on. I get the epub file of the book I wanna read. I drop it in calibre. The metadata is all over the place. I edit it to my liking, and export it as an epub file onto my PC. I copy-paste it onto my kindle through USB. The changes I made in the metadata are all present when viewed in kindle/koreader. Oops, I misspelled the author name, or I forgot to add "Fantasy" as a tag. DELETE the old files from both my PC and kindle. Repeat the metadata editing process, make the changes in metadata, export new epub file onto my drive, copy it onto my kindle.

check the book information in kindle...and it hasn't updated.

I'm confused. some people say using the "polish" function works. First, idk why it doesnt work for me, ever...second, I followed the same steps that I did when editing the metadata the first time. If the metadata wasn't drilled INTO the file, how were the first changes I made reflected on my device, but the second time I edited them, it wasn't updated?

Any help would be appreciated. thanks :)