Event Scheduled Reminders set for *Before* start dates won't send to participants registering *After* the start date
1) Yes.  If you have a reminder 2 weeks before saying "Just 2 weeks before our fabulous event ..." then you don't want that being sent to your last-minute registrants.

2) Yes.  Your before and after reminders are independent.

3) Not sure, but I doubt it.  If you set it before the sending time then it would be sent.  ie if it is now one week after the event and you configure something to go out 2 weeks after the event it should work.

Small updates to the docs are easy so if you can add useful information there, please do.