With respect to the Plastisol Plast PF Amex inks, what’s the difference between the three types of white?

The differences are as follows:
White is the classic printing white.
Dry Optical White is suitable for creating backgrounds for multicolour printing. It’s a very opaque white, therefore it can also be used as a “finish” white.

The Anti-Sublimation LB White is useful in situations where, when printing on synthetic materials (like polyester), a significant amount of ink is absorbed by the fabric. This ink creates an anti-sublimation barrier and can be used as a final white or, in the case of multicolour printing, as a primer.