Is it possible to run a new multi-level formula on the FALSE of an IF/ELSE statement?

I have a formula which checks if some cells are blank.

If one of the cells is blank, then the result is "". Simple.

If both cells are populated, then I want to run a formula (think of this as a checking step).

However, I keep receiving errors and no matter how much I tweak it, I seem to keep missing a step. Here is the formula:

=IF(OR(ISBLANK(W6),ISBLANK(W7)),"",("TRUE": "&ROUND(COUNTIF(T2:T13293,"TRUE")/COUNTA(S2:S13293), 4)*100&"%""))

The formula used to be:

="TRUE: "&ROUND(COUNTIF(T2:T13293,"TRUE")/COUNTA(S2:S13293), 4)*100&"%"

I simply added a few "checking" wrappers to validate the data before executing the formula.

How can I get this to work in the way that I want?