Hi there
Just to let you know there are a whole stack of Jerdan descendants in NZ. William Jerdan was my great, great grandfather and Mary Maxwell my great, great gm., his daughter Agnes - my great grandmother. She married Charles Martin, one of three Martin siblings who married three Jerdan siblings.. They had a family of 5 but the eldest daughter died. The family emigrated to NZ in the 1890's.
There is a book available written by Susan Matoff that can give you quite a bit of information.on the Letitia Langdon connection but you likely already know about this.