@chris17mom Hindsight is 20/20, but it’s a shame your son didn’t educate himself about the system a little better. It’s always a bad idea to decide on one group and one group only, particularly if it’s a fairly selective fraternity.
The process you describe sounds a little like “Formal Rush.” At some schools this is followed by Open Rush, a period of two or three weeks where bids continue to be extended. Some groups will extend bids after rush is over. It just varies from campus to campus. Have your son check with the Greek Affairs office and find out what he can. And should he have to wait until next year, encourage him to visit and consider as many groups as possible.