I suggest you reread the decision form Snyder vs Doe. It was NOT about getting off the registry. It was about applying enhancements to people who were convicted before the enhancements were passed.
Commonwealth vs Muniz is NOT about getting off the registry. It is about the retroactive application of the Adams Walsh Act.
The reason pre Adam Walsh Act people may get removed is due to Commonwealth vs neiman. Muniz is needed to not apply Adam Walsh Act retroactively and Neiman is needed to make the previously Megans law unconstitutional.