unfortunately I do not have nothing but a frame, i have also examine it carefully and i have not found any logos or numbers,
from seller i know that it could be a german bike, i searched around 10' - 20' as you suggested and i have found Göricke Nero Damenrad 1925 but not everything exactly match

my idea for this bike was to leave only rusty frame and composed all other parts from new chrome and shiny, but maybe such old bike is better candidate for restoration