I don't know and I did not know what I posted above until I tested it.
1) An assumption would be that the monthly rollover is a simple data arithmetic base on the expiry/rollover date.
Another is that there is some sort of adjustment to take the next or previous start of period from the rollover date and recalculate the next rolloever.
Then again it could be something different.
It has to be tested unless there is somebody who knows and shares this information.
2) I have had no reason to doubt that this far.
I have been happy to see that the slice start date in the definitions changes if I change is and then after a while the expiry date is displayed when the slice values are calculated.
The warning does not mean that
ALL the existing records from the slice table
but only the records for the revised request.
Martti K.