Kirkebøker, 1816-1928 Den Norske kirke

I think I remember somewhere in the past being told the reason that some church records were duplicated in Hurum, Buskerud and Strommen, Vestfold. Can anyone refresh my memory? I have two ancestors that show up in both as Christened, on different dates, but in the same month or so. This happens with only the first two of four children so think there was a fime frame of duplication. 1837 & 1838. The other two siblings born in 1839 & 1842 were not duplicated that I can find. Full detail as I have it: Kirkebøker, 1715-1928 Den Norske kirke. Hurum prestegjeld (Buskerud) Døpte b. 9 1816-1826 - FHL INTL Film 123953 Records Show: Father: Guttorm Torgersen; Mother: Elen Hansdr Torger Guttormsen Male Christening: 30 Sep 1836 Hurum Buskerud Norway Hanne Martine Guttormsen Female Christening: 22 Mar 1838 Hurum Buskerud Norway Jens Andreas Guttormsen Male Christening: 06 Oct 1839 Hurum Buskerud Norway Guttorm Edvard Guttormsen Male Christening: 12 Jun 1842 Hurum Buskerud Norway ================================================= Kirkebøker, 1816-1928 Den Norske kirke. Strømm prestegjeld (Vestfold) Døpte Kl.b. 2 1827-1839 1845 1847-1857 Records Show: Father: Gutorm Torgersen; Mother: Elen Hansdr Torger Guttormsen Male Christening: 05 Feb 1837 Strommen Vestfold Norway Hanne Martine Guttormsen Female Christening: 29 Apr 1838 Strommen Vestfold Norway Any insight would be greatly appreciated.