With the solution that I gave you, just enter the group name in the next column and copy the formula from the previous column to the right as far as necessary and down as far as you want. The new group will be counted for all names new and old.
If you want to add the capability in ahead of time so that all you have to do is to add the group name in Row 1 use this formula in B2 and copy across as far as you want and copy down. If the number of rows in the original sheet exceeds 200, increase 200 to whatever you need.
Formula:
=IF(OR($A2="",B$1=""),"",COUNTIFS(Sheet1!$A$2:$A$200,$A2,Sheet1!$C$2:$C$200,B$1))
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