So every pope since Vatican 2 was validly elected and then was deprived thereafter? Well, it might work with sedeprivationism, but it in no way aids that position or any sede position for that matter so it's hard to see how sedes could have any motive in pushing it.
Sedeprivationism is the only theory which lines up with all/most of the facts. The election-then-deprivation-of-spiritual-office lines up with the fact that both St Pius X and Pius XII changed the election laws to allow exactly this scenario.
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Meanwhile, sedevacantism has a plethora of reasons why the V2 popes aren't popes, with no consensus on the main reason, with no explanation of the above election law changes, and mostly using indirect logic (i.e. working backwards. Example: Pope was elected, pope spoke heresy. That's not possible, therefore pope wasn't elected in the first place). R&R also does not explain the election law changes, because they (generally speaking) don't acknowledge that the V2 popes are 100% heretics.