Any possibility?

My great-great-grandfather, Oskar Petersohn, was born in 1873 in Zeitz, Germany and lived there until 1893. Unfortunately, the Magdeburg archives were destroyed during the war, so there is no documentation for the years 1893–1899.

It appears that Oskar got married in England in 1901, and my great-grandfather was born there in 1905. I am aware of the “10-year rule” regarding citizenship.

Oskar and his family returned to Germany in 1907. (I have documents about that, and date based more less he leave germany was 1898, my great-grandfather started working on a ship in , although there is no official German document for this period, only a consular matriculation record.)

Back in Germany, I have records showing my great-grandfather living there from age 2 to 18, including school records, Arbeitsbuch (work card), and the registry for immigration to Brazil, though none of these explicitly state his German citizenship.

Regarding Oskar: after returning to Germany, I have birth records of other children from 1908 to 1913, as well as Melderegister entries from 1915 to 1918, indicating that he was recognized as German and served in the German military. Finally, Oskar died in Memel in 1943.

My great-grandfather later left his father and immigrated to Brazil at age 18. According to the rules, everything seems fine, but my difficulty is interpreting the “10-year rule” in this unusual case, given the gaps in documentation and the periods abroad.