We don’t have a figure for new publishers so we make do with the baptism figure as a close approximation. This is reasonable because most unbaptised publishers get baptised within a few years, and those who become inactive before baptism cancel themselves out in relation to the baptism figure. So in any given year the baptism figure may be different from the number of new publishers, but over the long term they follow the same trajectory.
Yep, "over the long term". The 2019 baptism statistics say nothing about 2019 pub number change, and year by year comparisons and calculations based on the numbers of baptisms are unreliable. But I think it's OK to use them to make comparisons by five-year periods and by decades. And again, it's better to use average (instead of peak) pubs numbers for this purpose.
The JW death rate is likely lower than the worldwide average because they are overrepresrned in wealthy countries and they don’t include infants as members.
I'm not sure. On the one hand, the mortality rate in Europe, Northern America and developed countries is actually higher than the global rate, and under-five mortality in these regions is significantly lower than among adult population. On the other hand, the death rate in Latin America is lower than the global one (source, p. 10 et seq.). I think it's only safe to say that the global mortality rate among active publishers is between 0.5% and 1.5%.