IIRC:

One trick they can use to shrink your itinerary to fit in the mask is to use the YY indicator (all carriers, all routes).

For example, if the first six segments of your ticket were:

LIS BA LHR BA DXB BA LHR BA JNB CX HKG (followed by 15 other segments, to equal 20)

They could re-write your itinerary as:

LIS YY HKG (followed by 15 other segments, to equal 16).

This only works provided you've flown the first segments, which your OP says you have. They should be able to get Sabre to automatically re-issue it by using this trick.