Genghis, I did a search for JSP318 without any luck, so got to surmising "why would it be so?"
The only seemingly logical explanation I could think of was one P1 had done the full conversion to type, while the other P1 (TP) was there to carry out a particular test, and not full bottle on systems, emergencies etc. Each was bringing a set of skills to the task that the other didn't have in effect.
Plausible?