perhaps an exaggeration or overreaction

It kind of bothers me when people call their subsequent month-long intervals of their relationship, their ‘anniversary’. Because in Latin, anniversary is derived from the adjective, 'anniversarius’ (returning yearly). Loosely it has been accepted as meaning “they’ve been together for a month” or whatever, but I feel as if this has only come about out of ignorance and incorrect application. I know it’s not really that big of a deal, but the degradation of language really bugs me for some reason.