ChemFinder: The Mol_ID is not re-used when the last record is deleted and a new record is added.

Mol_ID's are only guaranteed to be unique, not sequential mainly because the Mol_ID in an MSI file can not be deleted by record deletion. If you want to delete unused Mol_ID's and compress, you can export your ChemFinder database as SD file and import the database back to ChemFinder. This should eliminate Mol_ID's of empty records.