Do you mean that the Dogma of the Immaculate Conception was clarified (1854), and the the Assumption of the Blessed Virgin Mary (1950)?
Before those dates, those two items weren’t dogma. Now they are. Dogma has changed. Not that big of a deal, anyone can see that they weren’t dogma before and now they are. Just stop with the fiction that dogma can’t change. Perhaps it is more correct to say that ‘dogma, once promulgated, can’t change’.