Rectification Interval Extension
There is a function whereby the Rectification Interval (Cat A, B, C or D) MAY be again extended under certain conditions which will be detailed in the MOE / MME. As the MOE has to be agreed by the NAA then it is official. Cant remember where it is written but it can be done. I'll see if I can find a ref somewhere.
Other instances which are used are 1 ext for downtime to investigate then another for decision etc then another for repair time etc etc. that is a bit of a joke but the CAA has been known to allow it!