I think (I reserve the right to be wrong :-) the William Allen 1725 you speak of was actually William Hunt Allen who had a will dated 1781.William Hunt Allen is shown as being born between 1705-1725 and died anywhere after 1775...he actually had a will dated 1781, Granville Co, NC.So many Allens...with same name...it's hard to dig out who was who.
William Hunt Allen was son of Capt. William Allen of New Kent, VA son of Richard? Allen.From my own personal research, I am satisfied about the parentage of Wm. Hunt Allen and who his father was...after that, not so sure.
I have two William Allens, both born same timeframe, same area...one on paternal and one on material side of the Allen family...I still haven't figured out the paternal one.