Your ACR cache can absorb a certain amount of disk space, from which info for deleted images may not be cleaned out immediately. You can purge the cache altogether for a quick if temporary fix, or else trim its size limit. This doesn't need to be set very big, as of recent LR versions - I have mine set to 1GB. If you have LR do a catalog backup on a regular basis, e.g. each time you exit LR - these won't overwrite each other, and each is a full catalog copy rather than incremental, so they can accumulate without limit. They can likely be all cleaned out apart from the latest one or two, assuming regular independent backups of catalog and images of course (ahem). If you have at some point upgraded LR version, there may still be the earlier version installed. Likely not needed any more. Otherwise, images can be moved (within LR) to a new storage location on another drive, including a network drive, or on removable media even, rather than needing to be deleted out of LR altogether. That retains not only all latest edits (though those could be written out alongside the file), but also some organisational stuff, virtual copies and your edit history which cannot be written out alongside the images. The same Catalog can refer to images across multiple storage volumes, even volumes which may from time to time be disconnected. Lastly, if short of onboard disk space, the Catalog itself can be housed on an external drive instead of within the computer (but cannot be used from a network drive).
... View more