Luke M wrote...
....
Unfortunately, COUNTIF is not a 3d function. You can do it with a helper
cell though.
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=COUNTIF('TAB1:TAB5'!F:F,'Summary'!A2)
....

This is a typo. As you correctly point out, COUNTIF doesn't support 3D
references, so the formula above will return #VALUE! errors. You'd
need to use

=COUNTIF(F:F,'Summary'!A2)