There is no correlation between publishers and baptisms.
IMO this is too strongly worded. There's definitely a correlation, it's just that the number of baptisms will lag behind the number of new publishers. Looking at a single year the numbers don't mean that much to one another, but looking over a longer period I think one can fairly accurately estimate the number leaving. The number leaving might not always include those who were baptized at some point, but if someone becomes a publisher and then leaves I think we can still count it as a win for team TTATT.
I was under the impression that the "peak publisher" total was taken from any given month showing the highest publishers reporting. It would explain special campaign months where irregular publishers and even some inactive publishers are encouraged to engage in the campaign and report time for the month. That month would generate thousands more publishers in the ministry and would be used as the "peak publisher" mark reported in the yearbook
The last two Augusts have been good examples of this. I think typically they'll do some sort of reminder that it's the end of the service year and ask for any late reports to be turned in (thus concentrating the late reports in a single month to generate a false peak vs allowing them to come in whenever which would average out) but they definitely did that this year. Then in 2014 they had the big JW.org campaign in august. I think the reason for this campaign was primarily to allow them to post a significant increase in 2014 (which it did, the increase in publishers for 2014 was between 25% and 90% higher than the years prior) because they were concerned that any drop in numbers as a result of the arrival of 2014 would be detrimental to them. I think they're paying for it this year, though, because they can only artificially inflate the numbers like that so much before they reach a ceiling.
What percentage of active publishers are not (yet) baptized?
I'd estimate this at ~10% at most. In recent years it may well have gone down as the average age of baptism seems to have gone down.