[Ger-Poland-Volhynia] Julian and Gregorian Dates in Lipno Records

[LMPauling]

I have had the following inquiry from a correspondent in Germany and I do not know the answer to his question. I am hoping one of you more knowledgable people on our list may be able to give him an answer.

I did miss seeing you all at convention and hope you had a wonderful weekend!
Linda Pauling

I've noticed, that several documents of the Lutheran church records of Osiek nad Wisla/Osówka and Lipno (and also of Plock, Wyszogród and Sierpc) often show two dates during the period between 1826 and 1867, using the Julian and the Gregorian Calendar. But a not small number of documens show only one date for the named period, even though the Polish Kingdom was part of the Russian Empire at that time.

Is it allowed to use the Gregorian calendar automatically, if only one date is given, like in the period befor 1815? Or must the question of using one definite calendar stay unanswered, if there is no further spcification?