The citation for these records says that they are from the Dutch Reformed Church Archives, Potchefstroom. They are baptisms from 1915-1971, however, they are not only from Lusaka and it is not always clear where the baptism took place. Other places that are mentioned are Mufulira, Luanshya, Broken Hill, Krugersdorp, Livingstone, Kalomo, Bowwood, Chingola, Nkana, Zimba, Bulawayo, Chomo, Pioneers' Rest, and Tara. Some names seem to have come from registers in Rustenburg, in the North West province of South Africa.
I'm sure I've made many mistakes, and some transcriptions are just guesses, but this could give you the start you need to get into the register at the right place. If you have any corrections to my readings, let me know and I'll fix them, but I've tried to be true to what (I thought) I saw written down. (Earlier I did a rough trawl of names in these records, which I posted here.)
Image 21 in the FamilySearch records includes some duplicated records from the begining of the register as well as some baptisms that are not mentioned earlier, but also have no dates attached to them.
See the full list of names here!
https://zambiabones.blogspot.com/p/index-of-dutch-reformed-church-baptism.html
