The adjustments are shared publicly and readily observable. You can suggest they're wrong or they've lied for 80 years straight intentionally, which could be true, but this is an amazingly easy thing to falsify.

Just.. get an IQ test from the 1950s and give it to people.

Then.. if people need to ask questions.. they could. Given how simple this would be, why do you suppose you are right, and yet, no one has done it?