I think some nns do work on their own, often because they're different from the name itself and often because people are very used to just hearing the nn. Some I can think of off-hand:
FrankJakeJackHarryGeneTracy /
TraceyStacy /
StaceySadieMollyPollyDoraJudyKate /
CateNancyMarcy /
MarcieNell /
NelleNora /
NorahSallyLoriJillTanyaMoste -ette names:
Suzette,
Jeanette, etc.
Shannon