Here in the north, are there any chances that SHB in the ground, will hatch out in spring? My guess is no.
Or do they always pupate and then enter the hives for winter? yes
Coming out of winter, are all the SHB you see the only ones to make it? yes
If you were to go frame by frame, and kill as many SHB as possible first thing in the spring, would any future SHB come from missed SHB that over wintered and propagated, yes
or would new beetles be hatching out from the ground and re-infesting the hives? no
My answers to your questions have no data to back them. I will say that I have never lost a hive to SHB in the winter. I see lots of beetles in the winter but they seem to lay their eggs and slime the hives in the summer. It is like they need the cluster warmth of the hive to survive.
My two cents worth,