The translation of "pro multis" as "for many" vs. "for all"

[Historian]

You're making a very large assumption considering "for all" to render it doubtful.  Even those who consider it a grave scandal agree that it shouldn't change the validity of the Consecration.

For it to be invalid, the substance of the Consecration would have to be changed.  St. Thomas claims the substance of the form is: "This is My body,"  "This is the chalice of My blood."  That hasn't been changed in a significant way.

ST III Q 78 A 1