Thanks for new thread Monkey
Apologies for delay Shimy. I guess colleges have similar approach to % of over-offering as here, depending on what the legacy data shows for acceptance stats. But yes, multiple offers are potentially held until released back by May deadline. There can be a scrum between offers and acceptance day with colleges courting those students they don't want to lose with incentives to accept.
Don't think there is a firm/insurance, but, for international students they are allowed to accept one offer in May per country applied, and withdraw come A levels/results day. So in summary, you can hold and accept a US offer but decide to stay domestic come August when your results are in, accepting your UCAS place instead.