Sure.
1) Modify the formula in Subreport 1 to:
whilereadingrecords;
numbervar x := x + 1;
"";
2) Create a second formula with this code:
shared numbervar x1;
numbervar x;
x1 := x;
"";
Place both these on the Details Section
3) Create similar formulas in Subreport 2, however just change the shared variable name to x2.
4) In the Main Report, create a formula with the code below:
shared numbervar x1;
shared numbervar x2;
if (x1 = 0 AND {?Prompt} = "Stack 1")
OR (x2 = 0 AND {?Prompt} = "Stack 2")
OR {?Prompt} = "Stack 3" then
"No Data Available"
-Abhilash