[tbrownaw]

There are tables at $dayjob with both (begin, end) and also (incept, expire) fields. It's "on such-and-such date, X was true", but also allows for "as-of Z date, we believed that...".

Also you can have most data being currently unused even without being flagged deleted. Like if I go in to our ticketing system, I can still see my old requests that were closed ages ago.