Duplicate files · Scanning and Auto-scan
What do the numbers in the Duplicates status line mean?
Short answer: It shows how many duplicate sets were found (each set is a group of identical files), how much space removing the extra copies would free, how many files were actually compared, and when the scan ran. Small, hidden and in-package files aren't counted.
After a scan, the line under the source name sums up the result: how many duplicate sets were found (a set is a group of identical files), how much space can be freed by keeping one copy of each, how many files were compared, and when the scan ran.
The file count is the number of files actually compared — not every file in those folders. Files under 1 MB (unless Include small files is on), hidden files, and anything inside packages such as photo libraries and app bundles aren't counted, because they weren't compared.
"To free" counts only the extra copies; the copy you keep is never included.