Can you source this info? I'm curious to learn more.
OK, but let's clarify. The U-235 and P-239 cores won't deteriorate significantly in 25 years. But the tritium in the initiatior (i.e. the neutron source) and/or booster system must be serviced often to keep the weapon viable (I have no idea exactly how often, but certainly at least once every 12.32 years-the half-life of tritium). Also, someone collecting enough tritium to service 160 bombs would be noticed, since total world commercial demand for tritium in any given year is only around $30,000. A huge spike would be sure to raise red flags. It goes without saying that military tritium stocks are closely monitored and even governments that are unfriendly to us might not want to relinquish that much tritium to a terrorist group..
Another consideration is that nuclear weapons require a power source. They have large batteries that must be kept charged in order for the bomb to remain viable. You can't just bury one in a flower bed and forget about it. It would need a dedicated power line hooked into it.