I would be surprised if my mother didn’t know. However, I have no confirmation of this. My conclusion is more of a theory based on the preponderance of evidence.
Several years while my wife and I were visiting from out of state for a few weeks in the summer, my mother decided to be helpful, and fold a basket of our laundry, a loaf of underwear. It would have been impossible for my mom to have not noticed it was all panties (with no boxers), and panties of two very different sizes. Additionally, my mother fold my panties as I prefer, and my wife’s as she prefers.
However, my mother has never broached the subject with me, and I have not broached the subject with her. At first, I refrained to avoid putting her in a position of possibly having to lie to my father (who I very much believe would not approve). My dad has since passed (2 years now), yet the subject has not been brought to bear.