The 1981 Yearbook, pp. 31-32, states that Jehovah's Witnesses made "steady progress" in the years from 1974-1980 and it was only the number of Memorial partakers that decreased. Their chart, however, shows that in the years following 1975 there was a decrease in the average number of publishers, pioneers, and hours spent in the ministry. It was only after 2 or 3 years of decrease that the numbers started increasing again.
This claim of steady increase that was belied by the Yearbook's own chart upset me in 1981, and I've remembered it to this day. It seemed as though the Society were trying to get us to not actually see what the evidence showed and instead to take it for granted that it backed up their claims.
I was unable to reproduce the graph here. It can be found at http://www.watchtowerwayback.org/jw-wb/English/Books/Yearbooks/1981%20Yearbook%20(yb81-E).pdf.
Thanks again to OrphanCrow for the link.