Mary and Bess' shopping montage happens during a warm, sunny day typical of spring or early summer. However, exterior shots of Mary's apartment show that the house has snow on the roof and the trees are bare... indicating winter.
Mary tells Bess that her mother's first name is Marge. However, when Mary's mother is introduced in Season 3, her first name is Dottie.
From the exterior shots, they show us Mary lives in the attic apartment, however, early in the episode Rhoda explains she came "down here" from her place "upstairs", to meet Mary for a movie date.