yes i received my pgwp for 18 months rather than 36 months, due to my passport validity.You can only extend your PGWP if you did not receive the full duration of your PGWP due to passport expiry. In other words, if you were entitled to a 3 year PGWP but only received 1 year due to the expiry date on your passport. If you meet these conditions, then you should submit an application by paper to extend your PGWP.
"ISSUED TO PASSPORT VALIDITY" REMARK IS ALSO THERE