I'm reminded of the progression of Godzilla universes. The original Showa kaiju films were originally self-contained (numerous different ones treated their giant monsters as unprecedented) but eventually knitted into a loose shared continuity through return appearances and team-ups of the various monsters, so that everything from 1954-75 was essentially one universe. Then in 1984 they did a gritty, mature reboot that ignored everything but the original film, and over the next decade they made a total of seven films in a single continuity with recurring characters and eventually a recurring organization (and after that they did a separate trilogy of Mothra films in a different, Godzilla-less continuity). Then from 1999-2004 they did six films that were set in five different continuities (though all included the '54 original), but the last three (the last two universes) partially reintegrated elements of Showa continuity. Although the analogy breaks down there, since they never fully returned to Showa, and indeed the past decade has brought us two new Godzilla universes (three if you count the Legendary Monsterverse) that completely ignore everything that came before, even the original film. And don't get me started on Kamen Rider/Super Sentai "continuity."