I was also a bit confused by all the deadlines and terms used but was doing some digging today.
Plan to enroll (PTE) opened up near the end of February this year on the Choose Your Medical School (CYMS) portal on the AMCAS application. The school you choose for PTE can be changed until April 30th. If you have more than 3 acceptances, you should narrow them down to 3 by April 15th (not sure if that is required, just something I've seen mentioned). During the Feb-April 30th period, the school you select PTE for can see aggregate data for everyone selecting or not selecting PTE for them, but they do NOT know the specifics (exact names, etc.) You are not required to give up waitlists while having selected PTE, even after April 30th, but you do have to give up all other acceptances by April 30th.
The option to ommit to enroll (CTE) opens on April 30th and forces you to give up all waitlists and other acceptances too, so definitely do not select that when it opens up, unless you don't care about the WL anymore or are happy with your school
I believe you can stretch the PTE status until around June (school dependent, i think its around 21 days before orientation that you must CTE). After April 30th, I believe schools do know who exactly is opting to go to another school and who is choosing to PTE or CTE to their school. They also know whether waitlisted students have PTE or CTE to another school. They will not know what other schools accepted students choose to go to until after the cycle is done. I can't remember if the school that accepts you can tell how many waitlists you have.
Can schools you are waitlisted at see if you clicked PTE yet for another school?
I'm pretty sure they can after April 30th, but not between now and then (someone please correct me if I'm wrong).