Thanks for you response.

>>Are you allowed to enter a status for a date in the past, before an existing status?

No, but a date range could be split in which the start date would not change., so once a start date is established there will never be a preceding one.

>>Can you enter a status for a future date?

No

>>Are two statuses allowed to be effective and overlapping?

No

>>Must there always be a status for any and all points in time for the life of the row from when it was entered up until now?

Yes

>>Are status rows updatable? This can cause serious inconsistencies.

Yes.