I was talking to an acquaintance the other day and when she mentioned her young daughter Becca, I suddenly thought, “Hey, whatever happened to Becky?” You rarely hear of a Rebecca under the age of 13 these days who is called by that traditional diminutive.
This is something that happens with pet forms in general–they go through phases and changes as much as–or indeed more than–the mother name. For example when you hear the name Elizabeth, you have no idea of her age–she could be 99 or 9 months old–but you can certainly guess that Betty is a Grandma and that Liz and Beth are probably young adults.
Some other examples: Patricia‘s nicknames went from Patsy to Patty to Pat to Tricia to Trish to practically non-existent. The no longer popular Mary spawned any number of offshoots before it faded, including Mamie, Molly and Polly. Katherine moved from Kate and Katie to Kit and Kitty to Kay and Kathy, back to Kate and Katie, to the current Kat; and Edward launched not only Eddie and Ward but Ed, Ted and Ned.
But the prizes for the two names with the most mutable pet forms and offshoots have to go to Margaret and Elizabeth, many of whose diminutives have become stand-alone names. Here, in the roughest chronological order, is what Margarets and Elizabeths been known as over time: