Nuclear weapons small enough to be called "suitcase nukes" contain subcritical amounts of fissile material, and require a "booster" made of tritium or some other short-lived isotope as a neutron source. Over the course of a few years the tritium decays and is no longer able to boost the reaction to criticality unless it is replaced. And replacement is a high-tech operation, beyond the technical capabilities of anyone who isn't capable enough to build their own nuclear weapons from scratch in the first place.
At least one of the US nuclear tests in the 50's failed because the tritium booster wasn't up to snuff.
So the good news is that portable nuclear weapons have a limited "shelf life".
My understanding is that the Russian bombs in question were designed for operation by people who weren't rocket scientists (to coin a phrase), and, to have a decent storage life (or indecent, depending on perspective).
I presume they'd either have managed a way to cram enough uranium into it to not need a booster, or, to have a handy-dandy "drop new tritium capsule here" hole on the top, or, there could be something to the "red mercury" stories besides the mountains of disinfo and flapdoodle. (At least one noted American -- the guy who invented the neutron bomb -- believes that "red mercury" is for real. It's hard to write him off as a nutcase.)
Tritium has a half-life of about 12 years. Worse, it decays into helium-3, which soaks up neutrons like a sponge -- within a year or so, the chain reaction can't generate new neutrons as fast as the old ones are absorbed, and no earth-shattering kaboom.