Read a little further into your link and you'll find that https://en.m.wikipedia.org/wiki/Calder_v._Bull https://en.m.wikipedia.org/wiki/Calder_v._Bull gives a

Read a little further into your link and you'll find that https://en.m.wikipedia.org/wiki/Calder_v._Bull https://en.m.wikipedia.org/wiki/Calder_v._Bull gives a specific set of criteria for deciding whether a change is ex post facto or a retrospective "mollification". A grant of immunity clearly isn't included.