I think you're being too pessimistic. They're probably trying to underpromise so they can overdeliver. If they tell you these in-office events are once per year

I think you're being too pessimistic. They're probably trying to underpromise so they can overdeliver. If they tell you these in-office events are once per year, then they need to do it twice, you might get upset. Instead of asking them how frequently these things will happen, maybe you should ask how frequently they've happened in the past six months. Even better if you can ask someone not involved in your hiring process.