This winter, Eugenia Forteza and Mimi Klipstine faced a common inconvenience for those living in apartment shares: a departing roommate.

“We were like, ‘Oh, that’s a pain.’ We were so comfortable with each other,” said Ms. Forteza, a 28-year-old opera singer who became close friends with Ms. Klipstine, a 25-year-old actress and singer, after moving in two years ago.

But while they were dumbfounded that their roommate would want to leave their large and lovely three-bedroom in Washington Heights to move farther uptown, the apartment’s charms made it easy to find someone new, and Ms. Forteza quickly found a college acquaintance to fill the room. There was just one glitch: They hadn’t yet received their renewal lease, usually sent out months in advance.

“I just wanted the rent number so I could tell the new girl what her share would be,” said Ms. Forteza, who emailed the management company. “And they were like, ‘Oh, we have to talk on the phone.’”