Canon is a very simple thing. It’s everything that has been presented onscreen (excluding deleted scenes, unless incorporated later in something else). It has no requirement for consistency or the avoidance of contradiction. It’s simply the sum total of the productions.So in real life later canon rewrites previous canon?
Continuity is the thing you (and most people) are talking about things that appear contradictory to what came before. James R. vs T. Kirk is a continuity error. But both are canon. Kelvinverse and Prime are separate continuities. Both are canon. Etc.