I think you're right you can only PTE at one school, but I'm just curious who is enforcing the rule to narrow down to one school by 4/30? Like does AMCAS automatically withdraw any acceptances that you haven't PTE? The email says AMCAS "requests" you narrow it down to 1 Acceptance.
For the sake of everyone on waitlists, I really hope people follow the traffic rules, but it sounds like any penalty to not follow the rules comes from the schools themselves (ex. if you don't CTE by June 1st you're withdrawn from UConn). I am only saying this because I know many schools are delayed in financial info and therefore if there is no real penalty to hold multiple A's past 4/30, people might wait a bit longer until they have the necessary financial info to make those decisions.