As they say, the 18th time is the charm.

Or will it be the 19th time? Or both?

Either way, after designing the costumes for more than 125 Broadway shows, Jane Greenwood will leave Radio City Music Hall next Sunday with at least one Tony Award in her diminutive hands.

She has been nominated this year for her quick-change work on “Act One,” James Lapine’s sprawling adaptation of the beloved Moss Hart memoir. It’s the latest chance for Ms. Greenwood, who turned 80 the day after the nominations were announced, to revivify the fabrics and silhouettes of days past, notably the baggy brown suit that a young Hart wears as he hustles his way to Broadway success in the late 1920s. “He hadn’t grown into his persona yet,” she said. “That’s the sort of character work I like to do.”

Even more important, according to many of her collaborators, is her ability to give those actors the confidence and the background they need to pull off these period looks. After all, it’s not often that lighting designers or set designers ask the performers to strip down to their underwear for them.