Quoted in "The Making of Pride & Prejudice" by Sue Birtwhistle and Susie Conklin.

That said, I'll post some 1813 fashion plates of ballgowns to compare with Miss Bingley's numbers. I don't think the designer really appreciated the nuances of year-by-year fashion differences, because the 1813 styles were quite unique for ballgowns.

Louisa
Mistress of the Garderobe