Not a metallurgist, but I believe the concern is described as 'CREEP'.
When artificial stress(our sizing) is removed the brass recovers it's strain, releasing most energy added, -but not all of it,, and not all at once.
It may be prevented from doing so by it's grain structure. However, over time, there can be grain boundary sliding which can allow further deformation (from what seemed stable at first).
This is more likely to occur in work hardened brass, as there are more grain boundaries present.
There are 3 places I've run into it in reloading: Neck sizing, shoulder bumps, and primer seating.
What I've seen is continued countering of last sizing action, over time.
My last action with necks is normally expansion, and a month later neck ODs reduce further(~1/4thou).
If my last neck action was downsizing, then I could expect neck ODs to grow a bit over time.
My shoulder bumping is 1thou for immediate ammo use, but I've learned to go 1.5thou for stored ammo.
Similar with primer seating, I seat to 2thou crush, but this reduces over time. So for stored ammo, I go 4thou crush.
I'm sure I could anneal necks & shoulders more often to mitigate this.
Nothing I can do about primer cups/pockets other than compensate.
As far as neck tension, I do not believe creep affects it -while necks are at 1thou or more interference to bullet seating.
If your last neck action was downsizing to leave only 1/2thou interference to bullet(after spring back), then I would worry about tension, or at least pull friction, dropping too low for stored ammo. In a couple months you could probably pull those bullets by hand.