I think the majority of people rely on the Bitcoin node software to do the calculation of how many bitcoins are in existence. I think most people rely on the math and don't try to verify the supply themselves. And if they are relying on the math to be correct for Bitcoin, then they can rely on the math to be correct for Monero. Monero has asymptotically zero inflation in order to keep fees low and yet still manage to keep the monetary supply under control because coins will be lost over time and it will hit an equilibrium.