Jeannethe,
Precisely the Min and Max functions are intended for working on a set of 0, 1 or more values (0, 1 or more measured dates) over a common set of values of the dimensiones ("Facility" in your case) . What the test showed us is that the Min and Max functions are working fine when you do not discriminate on positive or negative checks.
The test suggests us that the problem might be that the check variable isn't working as intented. If you can make the [check] variable work you'll have your problem solved with the technique I suggested.
I'd recommend to test this check variable and all your intermediate variables adding a new table in your report with all the dimensions and measures your data contanins, each one as a column, as well as your defined variables, including the [Check] variable.
With this maximum detail of the data you can verify that all the variables including [Check] are working fine, the latter showing 1 where you know the check should show positive