Hello Neil
I am descended from a William Dyer, probably the one you mention as being born in 1772. If he is the same William who married Mary Pennington at Plymouth Charles in 1791, then I am descended through their daughter Mary Dyer (later CHOWN).
I think it depends on how prolific the name was around that time. If there were lots of Williams born in Plymouth around 1770, then I may be wrong.
The CHOWN family that Mary Dyer (b.1794) married into were fishermen and lived in the 'Elizabethan House' at 33 New Street amongst other houses in the vicinity.
Cheers - Michael.