Don't make the mistake which I did, there are two Derwens! one is a village a few miles due west of Llanfair DC close to Corwen, the other is the now defunct parish of Derwen Llanerch (often refered to as just Derwen) which is less than a mile east of Pentrecelyn where Rogers families later farmed (Pendyffryn, Pentrecelyn farm, Fron Ucha etc.)
David