Wouldn't the argument boil down to planned and actual?
In other words, you're sitting back at your base FAJS after legs 1&2 and now you have to repeat them, but you KNOW before leaving base on leg 3 you are going to exceed FDP on leg 4. Doesn't that mean you are planning it? You may be feeling fine before leg 3 but what if its a bit taxing and you end up at FADN not quite as bright eyed and bushy tailed as when you left FAJS? And what if there were then further delays at FADN.
Surely the correct thing to do would be to inform the operator that you will be out of FDP at the end of leg 3. Then, should you arrive at FADN and NOT feel up to leg 4 they cannot hold it against you and in the same light if there were further delays at FADN you couldn't be held responsible for running out of exceedence time.
After all, the exceedence time is a buffer zone, and to knowingly go into that when there is an alternative solution (standby crew), defeats the purpose of it.