panties or dk's over garters
As a more mature lady, who has learned a lot about ladylike dressing from her grandmother who had her own foundation wear shop, I know it was common, in the days ladies wore girdles and nylon stockings every day, that their panties, bloomers or directoire knickers where normally worn over the garters, to be able to go to the bathroom. Only in fashion magazine adverts as well as cheesecake pics panties where worn under, to give it a better look.
Over or under, depending of the length of the garter
I never wears pantyhose.
As for stockings and garter belt, usually the panty goes over.
However, when you have short stockings and long garters, I sometimes put the panty under the garters, because in this case, you can still do your business without unclipping the garters.