This is an extension of this question, which was answered by XOR LX.
In the original question, I wanted to count the number of rows in a matrix that included values that
@PyjamaNinja has encouraged me to try and develop my 'lemma' to their earlier question.
The method is:
A Count rows with entries in all specified columns (A-C and F-H)
B Count rows with entries in all specified columns that do _not_ meet any of the criteria in the columns being evaluated (A-C).
Subtract B from A.
=COUNTIFS(A1:A5,"<>",B1:B5,"<>",C1:C5,"<>",F1:F5,"<>",G1:G5,"<>",H1:H5,"<>")-COUNTIFS(A1:A5,"<=2",B1:B5,"<=2",C1:C5,">=2",F1:F5,"<>",G1:G5,"<>",H1:H5,"<>")
With many thanks to @XOR LX.