Unfortunately, there are several aftermarket coil module manufacturers out there, none of which are the same electrically. The tester was designed to test the AC module. Aftermarket modules will give you inconsistent results, being as they are not electrically similar. Some won't even produce a tach signal.
The goal is to find an OEM NOS module and HANG ON TO IT as it's become a rare item. It's the only module that will run your turbo engine correctly.