One hornet can sting multiple times, they have no barb in their stinger so they can pull it out and reuse.
Tell me about it.
The odd thing (to me) is after the ground yellowjackets sting quits hurting, the area will itch like crazy.
Follow-up. The "professional" came over and sprayed some dust (hmmmmm) into the hole. They're gone today. No activity at all. In fact, I cut the grass yesterday and didn't see any "jackets".