Calibre has two builtin date columns:
- last_modified: This is the column you talking about that gets updated whenever a book is modified.
- date: also called timestamp. This is the date the book is added to calibre and is never modified automatically by calibre. You can modify it yourself if you choose to, but calibre does not touch it.
If you want to have more granular control over date columns, check out the
Last Modified plugin. It allows you to assign different custom date columns to certain events.