German citizenship law has changed quite a lot. You are allowed dual nationality if you are born to German parents, whether in or out of Germany. You are granted German citizenship if your parents were non-citizen German residents living in Germany, with the caveat that you must choose only one nationality upon turning 21/23.

Up until around the 60's or 70's German citizenship was only passes paternally, but it not can pass through both the father and/or mother. There was no concept of jus soli before 1990. https://en.wikipedia.org/wiki/German_nationality_law#Birth_i...

I had to submit FOIA requests for records going back to the 1950's, as well as retaining a lawyer. The process took three trips to the German embassy, 18 months, and roughly $2000.

However, once the initial process was completed for myself, processing it for my children took a single trip, no lawyer, and roughly $100 apiece for application fees.