TD - it might be worth re-reading the recommendations about the ducting and noting the following:
Recommendation
The ruptured duct is replaced with new manufactured items on a fleet-wide basis as soon as possible.
Action Taken
Recommendation closed. All such ducts fitted to in-service aircraft have been replaced with newly manufactured items.
The way I read it, all such ducting on in service Nimrods were replaced in the aftermath of the investigation. The later paragraph you quoted that refers to a replacement program starting in Dec 07 refers to the lifing of the new ducts - therefore the ducts that were replaced after the investigation will be lifed, and replacement of the new ducting will start from late this year.