Interesting about the hard & fast rule of not exceeding the MR hours.
In NZ you can overun by 5% of the check. That is technically to allow you to fly your plane to a place of maintenance but it is widely used to allow booked flights etc to be carried out til it can go in for maintenance. The overun hours are of course taken off the next cycle, i.e overun by 5hrs next check is due in 45hrs.
This practice is avail to all operators, Private & ATO. Not sure about large 121 operators tho.
S2K