The inspections were purely a stock take. Missile 1990-cccp-100 still in silo 123 in Buttfuck Siberia. Tick.
Looking at a missile from 25m away will not tell you if the tritium has deteriorated past usability, now will it tell you if the electronics have failed or components corroded past usability.
The closest to an inspection done is that one treaty (there are several arms limitations treaties USSR & USA signed which Russia continued, plus ones signed by Russia post USSR) limits the number of warheads in total that multi launch vehicles can have, so they get to see the warhead rather than just a missile.
The warheads could be full of cotton candy as far as the inspectors know though, again, count devices, check against list.
NO american is testing the functionality or capability of these weapons.
Even if you doubt me (and I can dig out sources) here’s a thought experiment:
Would the US sign a treaty that allowed Russian engineers to dissassemble and test the functionality of a US nuke ?
If you think they would I have a nice one owner bridge going cheap.