There's nothing to doubt about it. It's what they did. They absolutely engineered several model-specific pickups using the same, or similar, die cut fiberboard flatwork as Strat pickups, but different magnet heights, magnetic polarities, and winding directions, specific to different models. They sourced the different parts needed to make the different versions. They absolutely did install these pickups in different models of guitars based on these differences in the pickups. They did not just mix and match Strat/Musicmaster/Mustang/Bronco/Duo Sonic/Musicmaster Bass pickups.
Stick a pair of '50s, '60s, or '70s Strat pickups into a Mustang or Duo Sonic with classic wiring, and the guitar will not even work as intended polarity-wise, not to mention being brighter, because the coils cannot get as close to the strings. Stick student model pickups in a Strat, adjust the outer two pole pieces to the same distances from the strings as they were on the Strat pickups, and you have a warmer tone than the Strat pickups, because the coil is sitting closer to the strings. Stick a '70s Strat pickup in a Musicmaster Bass, and you have a thinner sound, with an E and G string that are out of volume balance with the A and the D strings (somewhat like a flat poled Jazz Bass is) – already explained in my first post in the thread.
I have never said that these pickups are not inherently similarly constructed, or not made of the same types of components, in the general sense. All mass production shares parts whenever possible; it's basic efficiency. Even so, Fender's engineers deemed these differences worthwhile enough to source the parts for, and produce, the different variants, and place them each in specific models. I have said that they each had their own designs, intended for specific models, therefore they should not all be called "Strat pickups." That's not a controversial point. The variants were model dependent. Calling them all "Strat pickups" glosses over the differences, which are real. Musicmaster Basses did not use Strat pickups. They used Musicmaster Bass pickups...which were very similar to the student model guitar pickups...which were themselves very similar to Strat pickups. So...they aren't Strat pickups. Simple.