True, Buckhorn. If the shooter wants to peek at the tang barrel selector they can defeat the test. For me, it would be difficult with my prescription shooting glasses as it is very difficult for me to read things up close. I don't think anyone is proposing a double blinded scientific study and is it that difficult to remove your set screw.
Similarly, if you swap the chokes it would also be best if the shooter doesn't know which of the two mods are in which barrels. He may be able to look and partially defeat the value of the test (if he can tell the two apart) but why would he?