Such occurrences were not peculiar to Jewish citizens.
My grain of salt:
My father was born out of wedlock in England in 1916 to a C of E mother. My grandfather, a Belgian soldier wounded in 1914, had been cared for in the nursing home run by my grandmother, and when deemed fit to leave had been sent to several French camps in succession, probably before either of them knew my grandmother was pregnant. My grandparents married in 1917, but I discovered (after my parents had died) that my father's birth was registered with the GRO only in 1932, by when the family was living in Belgium. Apparently my father was taken out of school aged 16 and trained as a furniture designer, possibly in apprenticeship, and would have needed something more official than a baptism certificate to certify his date of birth.
And naturally, by the time I discovered this, all those who might have shed some light on the matter were no longer with us.
Happy hunting nonetheless,
Nicole Heymans, near Brussels, Belgium