That's insightful because it means it may be strictly an accounting issue versus an actual reduction in the number of warheads i.e. the number of warheads counted == the number mounted, not the total number possessed.
The number of mounted warheads is a very important issue, because a nuclear war will take at most half a day. So all the mounted warheads at that point are the ones that can be used, nothing more.
Of course if the war doesn't come as a surprise but with a lot of buildup, then you can remount everything over a few weeks.
The number mounted matters cause it determines how missiles can be used. With multiple warheads, ICBMs could be used for first strike. First strike won’t work, but opponent still needs to worry about it. With one warhead, ICBMs are only useful for retaliation strike.
Also, the US is still following New START treaty after Russsia pulled out.
