Especially when I read church records dating from the month of December from the 18th century or earlier, I always have to remind myself to be careful or I'd be in danger to mix up the dates.
Today is the first Advent sunday of this year's holiday season. We'll light the first candle on the advent wreath today, and this is really a sign for me that I'd better get started with my christmas preps.
In earlier times, Advent meant even more than this: It was the beginning of the new church (or liturgical) year.
As a result, children that were baptized in December were recorded as being baptized in the new year's records. This is because the liturgical year differs from the Gregorian calendar which was (and still is) used in a secular way. For example: If Anna Ilsabein Tubbesing was born December 2, 1757, and baptized three days later, you'll find her baptism entry at the beginning of the church records for the year 1758. Usually, the minister would mention that indeed she had been born in 1757, but sometimes he simply wouldn't bother and you need to make that mental leap yourself.
I really had to get used to this. And you really don't want your sources to get mixed up, do you?
Later on, from about 1800, the ministers started the new year's records with the first child baptized in January. This made it really easier... for them as well as for us!