I'll take a shot at refuting PART of it.
The Swiss have found a few caches with ordinary materials (radios, explosives). They were buried with a booby trap and pretty much ignored. This led to some fun issues (the Russians couldn't find some of them after a few years, plus the booby traps became VERY unstable).
But nukes need constant maintenance--and every trip to the cache risks exposing it to discovery. And if the authorites find a cache and disable the booby traps, then the USSR suddenly has a huge problem: it's pretty obvious that it's a Russian nuke. Can you say "foreign policy fiasco?"
If the Russians merely leave the bomb lying there, then they risk someone finding it and activating the anti-tampering device...and we now have a radiological disaster.
Rule One of nuclear weapons is: "Never take ANY chances with nuclear weapons security." Leaving them lying around unattended in your opponent's territory is a fairly gross violation of Rule One.
Also, imagine Elmer Lee and Clem finding one of these nuclear weapons caches, and somehow getting past the booby trap.
"Hey, Elmer Lee, I don't think we should be messin' with this. That writin' looks like that thar Sir-Rill-Ick the Russkies use. Maybe we oughta call the Sheriff."
"Clem, hold mah beer and watch this!"
Rule One of nuclear weapons is: "Never take ANY chances with nuclear weapons security." Leaving them lying around unattended in your opponent's territory is a fairly gross violation of Rule One.
Nobody ever claimed the Rooskies were smart. I could see if it were a couple of KGB or GRU "extremists" who pulled it off, and later got caught.
Barely.
Can't prove a negative. If they're not here, we'll never find them.