When people are studying, they become publishers and are counted as such when they report. Then the number of publishers would increase but without a addition in the baptism number.
Then when the person gets baptized, maybe in another service year, that person would be counted as a baptism and still a publisher. There is no correlation between publishers and baptisms. Children could be publishers for years before getting baptized.
Publishers are counted for each slip turned in in a month and reported to the branch. All the months are totaled and divided by 12 to get the average publishers for a year.
When people turn in reports late, say from April then in May 2 reports would be counted for that person. There would be 2 publishers counted. Enough of those gets the numbers up. That way it will average out but the peak is the highest individual month of reporting.