Proof that it was installed and working correctly is super easy. Multiple airlines fly the same route. The airlines should be feeding the data to the government and the government can cross-validate that the data is legit for routes that have more than 2 airlines. + the jet stream is quite large so even not the exact same route should still be able to highlight airlines doing fraudulent data by. If they’re not sending data, that’s also super easy to tell.

At some point the cost of trying to lie and cut corners becomes worse than the cost of compliance and the airlines and airplane companies will just become good at doing a good job here.