Sorry, I was thinking while typing, rather then presenting an 'idea' as complete.
Firstly I think there is always going to be a natural plateau with anything - a 'maximum reach' - religion included. What would be interesting would be when that plateau starts to fall.
(In product marketing, with a saturdated market where you've plateaued on you maximum market reach you look to use the brand name to expand the product range, sometimes into quite seemingly unrelated areas - actually an argument could be made for JW Broadcasting being that expanision - anyway, back to the main point)
While I thought initially that the maturity of the religion in those countries it has been active in the longest will have reached a plateau, you would still expect ongoing growth in those countries it hasn't been active in for as long.
But as my global increase figures, that doesn't really seem to be the case.
Excluding the anomalies of very low publisher numbers and high ratio countries... It seems interesting there's really only three significant countries reporting similiar increases to Britain back in the 1980's, namely
Angola 1:210, 111,123 publishers, 8% increase
Philippines 1:499, 199,551 publishers, 5% increase
Russia 1:832, 172,977 publishers, 5% increase