"I'm curious to understand the mechanics of how the ladies from long ago were able to keep a pad in place."

Orgone.

"Orgone was seen as a mass-less, omnipresent substance, similar to luminiferous aether, but more closely associated with living energy than with inert matter." ...orgone was conceived as the anti-entropic principle of the universe, a creative substratum in all of nature comparable to Mesmer's animal magnetism."

By concentrating Orgone in the genital Chakra through breathing exercises ye olden-day ladies could use the animal magnetism inherent in the orgone to act on the natural cotton of the pad producing a lift vector. The lift vector, functioning at 90 degrees to the longitudinal axis of the pad, gently but firmly levitated it onto the under carriage via "spooky action not at a distance." Through Orgone stacking of other energy centres in the body this technique was also useful with natural decorative merkins, non synthetic wigs and nipple pasties.

Sanitary belts were a thing as recently as the 1970s. Before then, I'm assuming that's why they wore layers and layers of clothes.

I have no idea either.