It's simple
The physical task of locating and pulling the CB is simple. In fact, in the operation I work with it is done after every flight.
I do not know the situation of the 767 crew you refer to. However, after any incident there are many non-routine items that must be accomplished. There may also be (usually is) a company requirement for you to immediately accomlish a drug test. So, off you go to the clinic (after completing a ton of paperwork and phone calls), and perhaps you missed that one step of pulling the CB. Nevertheless, even if you did pull it, perhaps maintenance pushed it back in as part of their normal reposition of the jet procedures.
In any event, I understand information can still be obtained from the tape, even beyond its intended time period.
If you are suggesting the crew did not pull it intentionally (this would not be my guess), you (and they) would have to be unaware that there are other ways to get certain types of information.