Someone correct me if I’m wrong, but I think for DIII and many schools that do not offer athletic scholarships there is no National Letter of Intent NLI to sign. It’s all verbal. As @leennp implied that means things can change on either side. The kid can decide not to swim or go to another school, or the coach can take on other faster kids and leave you out. I suppose you have to keep in mind if you want to go to the school you make a verbal commitment to, even if you do not swim.