If it’s not held in the table, where would the API pull it from? Are you talking about the last time the api was modified (which I doubt).
I think last modified time addition to every table is perfect and the only way to capture the last time a record in a table was modified.
createdTime is always included, regardless of whether or not a column exists for it on the table. If you look at the example JSON I provided, “createdTime” is not inside the fields object, but at the same level as “id”.