Removing old core versions

When a new version of the core is released I go through and remove the old one like this
sudo snap remove --revision=2312 core
This has worked well in the past however when I removed the revision above there are still remnants left:
/dev/loop3 81M 81M 0 100% /media/chris/disk
/dev/loop9 81M 81M 0 100% /snap/core/2329
/dev/loop1 80M 80M 0 100% /media/chris/disk1
The first two entries appear to be the same core version though the file dates are a bit different. The third entry is the previous core version 2312 apparently but if I removed it why is it still shown?