Things turn up.

      I have no idea how it arrived; unless buried amongst some equally old photos.
      I seems the eventually did "Carry out this Class of work ˜ ˜ ˜ " because Dad retired from that site still working as a "Motor Coach and Body Builder one or two decades later.
      In retrospect - 2-3 days later.  When did you last see "per pro" in full?  I have come across what I'll refer to as "people" who
A) Hadn't a Scooby what P P stood for.
B) No wiser as to what it meant.

      We live, AND learn.   (:¬o).  Neither, it would appear, did I!  I was taught, but not at school, that it meant "For, and on behalf of".
       I suspected it might be an abbreviation but never checked.
"per procurationem"  -  "by proxy" 
"The meaning of PROXY is the agency, function, or office of a deputy who acts as a substitute for another."

Maybe, as Mam, who probably herself inherited it, use to say 
"It's t'syam dog; weshed!"  For non-locals/"furriners"
"It is the same Dod - washed."