I searched the Irish Family History Foundation's database for Co. Louth and all Ireland. It now contains abt 60% of all surviving B/M/D rcds. Rcds B4 1840 are sparse.
I couldn't find B rcds for Richard or Thomas Grills (+variants) in either Louth or all Ireland for the right era. I also couldn't find a marriage rcd for Thomas for the correct era. This surname only has 66 B and 127 M rcds for 1700-1921. The B/M numbers are usually the reverse.
I conclude the B/M events for these people: 1) weren't rcd'd 2) rcd'd but lost 3) remain somewhere in the mass of undigitized rcds.