Yesterday I saw a little book "Strasburg Lutheran Church Records", George M. Smith & Klaus West (1997).Translated from the German.On 28 Oct 1771 a "Martin Barth", age 20, was confirmed.On 30 March 1777 Martin Barth was a godparent to a baptism.It's not clear if this was the son of Zachariah Beard or a diferent Martin.
However, Christian Bardt, born 7 January 1796, son of Martin and Elizabeth Bardt was baptized in 1796.Appolona Bardt, born --- November 1796, daughter of Martin and Elizabeth Bardt was baptized in 1799.
We know that Martin Beard's wife was Elizabeth when he sold his share of his father Zachariah's land in 1797, so this appears to be the same person."Bardt" was evidently the German spelling, "Beard or Baird" the English spelling.
This Martin Beard moved shortly thereafter to the part of Washington County, Va. which later became Sullivan County,Tennessee.He died there in 1814.
Does this match the information you have on your Martin?