I want to attempt to shed light on what I think is a reigning confusion on this and other threads specific to Plan to Enroll (PTE) and Commit to Enroll (CTE). The confusion centers around whether these are non-enforceable guidelines and/or are they mandates, and if the latter who enforces the mandate.
The answer, in short, is they are both. Let me explain.
Some schools, like UC Irvine, PTE and CTE are SUGGESTIONS, with no penalty for non-compliance. So, in theory, you could carry multiple acceptances and WLs right up through the CTE. In UCI's case, you can carry them through orientation. It seems strange but I think it is true.
Other schools, likely all of the top 20, perhaps more, and certainly some of the other UC schools like UC Davis and UCSF, PTE and CTE are MANDATES. For PTE, you must withdraw all other acceptances. This is not a guideline, it is not a "should", it is not an "ought". It is a "must". Obviously, you can carry WLs. With CTE, all WLs must be withdrawn. Non-compliance can result in a rescinded acceptance. This approaches, in my mind, a kind of contract. I believe it's enforceable by the school. Let leave aside, for the moment , whether the schools have the information to enforce it, but they certainly have the right to.
Much of what I have described above is available to accepted students on the AMCAS school-specific pull down tabs, if you have an acceptance at that school. There are posted screen shots in various SDN school specific threads.
If what I have outlined is true, there are almost no students who have PTE'd at mandated schools carrying multiple acceptance, and none who have CTE'd on any WLs.
A different story for schools that treat these options as suggestions. People can legitimately carry multiple acceptances and WLs after PTEing and multiple WLs and perhaps multiple acceptances after CTEing.
I believe each school has a strategic reason for choosing their path, even if one path comes with more uncertainty.