Sorry, I tought that you meant the baptism/civil register difference (july/october)
"My point being: Joanenes birthdate 16 Jul, 1798
Jan birthdate 10 Jul, 1798"
Joannes or Johannes (Latin), Jan (Dutch), Jean (French) and John are the same first names.
I think that Jan (first name really used by himand his family), born 10/07/1798, was registered as Joannes in the civil registers on 16/07/1798 and baptised as Joannes in october of the same year.
Reread the civil registration and you will probably find that the document was written the 16th (mentioned somewhere at the beginning van the document) and that he was born the 10th (mentioned in the middel of the document).
Jean/Joannes should be used in official documents until 1815 and possible again from 1830 on.
Jan/Joannes is normally used in 1815-1830 and could be used from 1830 on.