If he can't plant them in time for them to get their winter chill in the ground, or if the ground is frozen by the time he is in his new house, he might have to do what I do in zone 10, put them in the refrigerator for 6 to 12 weeks prior to planting.

If your dad plans to move locally (not hundeds of miles away and into a different growing zone) could he rent/trade for part of a friend's or family member's veg garden and get the bulbs in the ground as usual but in labelled rows?

I know you said 'hundreds'; however, could he separate out the late-season bulbs (think N poeticus, for example) and pot them up?

That way he could 'easily' trans-ship the potted group to the new yard; and

dig up the early flowering species and varieties 'in the green' for moving to his new yard. That would give the person who has let him use their yard a freshly dug patch for the coming season of veg planting.

As your zone is getting toward 'crispy winters' he would probably need to rig some sort of outdoor shelter to repel frost/snow for the potted set - bales of straw could be useful, with a weatherproof cover over and tied down.

Late planting is probably not going to work too well because of having to wait for the ground to warm up/dry out. By which time the air temps will collapse the flowering season, and trigger the onset of dormancy in the bulbs.

The fridge option is out, simply because my parents don't have a second one to dedicate to all the bulbs.

The move is local. I'll suggest the idea of temporarily planting them in my gardens and/or the gardens of other family. We all live in the same zone, so I don't think that would present any issues.

Thanks for the suggestions.