Most Catholics misapprehend propositions from commands. Propositions are either true or false. Mary was conceived immaculate, the proposition is either true or false, and I either believe it or I don't believe it.
A command is, "Bryan, don't you marry that woman, I warn you." Now, if we elope and run off to some 90-year-old, pre-Vatican priest and get married, it is valid. The command was given to the SSPX, "Don't you ordain those bishops." Putting the pope question aside (is he pope or not), the consecrations are valid. I have never understood the hubbub about operating illegally. We are dealing with pretended churchmen who violate Church law on the regular, meanwhile telling us traditional Catholics that we are bad people for not following the law.