When I received a single irregular tomestone (from the "Any Way the Wind Blows" GATE, in case it makes a difference) the message I got was:
You receive 1 an irregular tomestone of genesis I.
For consistency with other messages, it should say:
You receive an irregular tomestone of genesis I.
There was no problem when I got multiple tomestones from the "Leap of Faith" and "Cliffhanger" GATEs:
You receive 4 irregular tomestones of genesis I.