It says NW which I took as North Wales, Pembrokeshire is more mid or south.

Pwllheli is in the North Wales.

Edit

Scrub Dartford

I think John might have been born in Nantwich near the North Wales border perhaps.

WILSON, JOHN FREDERICK WILLIAMS
GRO Reference: 1859 M Quarter in NANTWICH Volume 08A Page 279

Oh for crying out loud no wonder you're having trouble, there is a James Wilson born in Pembroke MMN Williams.

Name:
WILSON, JAMES WILLIAMS
GRO Reference: 1863 D Quarter in PEMBROKE Volume 11A Page 670