When setting up an ABS it should be generating bookings also for dates earlier than today. When scheduling people sometimes the bookings rolled out need to be back dated. So on the 4th of a month perhaps a new ABS is setup for a user that should have bookings from say the 1st of that month. Today that can be setup in the ABS recurrence pattern, including setting the correct date - but bookings will only roll-out for today (or even starting day after). Not perfect (and actually a little confusing.)