Foreign inspectors might warn the Russians about the risk of theft, accidents and so on. But would they warn them if they noticed that the weapons were degraded or nonfunctional, unbeknownst to the Russians?
No, and that's kind of hard to assess - but if they are inspecting facilities for maintainance of nuclear weapons and they appear to be in good order, then it would be weird for those facilities to not be actually used for their stated purpose of weapon maintenance. No one, not even the russians, is pouring billions into keeping those facilities operational and up to scratch and then not actually using them - I think it would be very unreasonable to assume so.
It is hard to assess, so this is just speculation, but I would guess that it is far easier to keep a facility in good working order, shining, nice and presentable when you don't actually use it but just pretend.
Also, the Soviet Union as well as Russia do have a culture of corruption, plan-fulfillment-only-on-paper, diversion of public funds and organized inefficiency on the job. E.g. from the current Ukraine-Russian war, there are reports (to be taken with a grain of salt of course, but there are dozens of confirmed, similar stories from Soviet times) of food shipments containing just canned water instead of canned meat/vegetables because somebody embezzled the money and shipped water to cover it up. I can't really decide either way: maybe all this is even easier, given the secrecy surrounding everything military and nuclear. Yet maybe it is harder, given the increased scrutiny around all things nuclear.