Catholic Culture, Phil Lawler:
The US Constitution (Article I, Section 9) prohibits ex post facto laws. A legislature can make an activity illegal, but it cannot make the prohibition retroactive: you cannot be punished for doing something that was legal at the time you did it.
The Code of Canon Law has a similar provision. Canon #9 states: “Laws concern matters of the future, not those of the past…” But the sentence continues with an important qualification: “… unless provision is made in them for the latter by name.”
Since I claim no expertise in canon law, I cannot offer an informed opinion on whether a canonical requirement that is imposed today applies to actions taken in the past. But that question now seems relevant. Because the Vatican today issued a document that seems to impose a requirement— a further restriction on the traditional Latin Mass— that did not previously exist. Report is here.