The WTBTS are quite dishonest in how they report the figures from the middle of the twenties.
The Proclaimers book implys that the decrease was only in a couple of countries :
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Following 1925, meeting attendance dropped dramatically in some congregations in France and Switzerland.
God's Kingdom of 1000 Years is even more dishonest , describing the increase to 1925 as a fulfillment of prophecy & sign of Jehovah's blessing without stating that the number of Bible Students decreased dramatically after this date..
kachap.12pp.236-237pars.54-56Increasing the King’s Belongings The annual celebration of the Lord’s Supper on the following date, Wednesday, April 8, 1925, brought something encouraging to light. Because of the planting, watering and cultivating work that had gone on till then in additional areas of activity, with the newly provided instruments for Kingdom publicity, the number of congregations of disciples with heavenly hopes increased. The membership of congregations increased. So at this celebration of the Lord’s Supper the number of participants therein indicated this growth and production of disciples of Christ. How many, then, did participate that year? The September 1, 1925, issue of TheWatchTower, page 263, under “Memorial Reports,” says: 55
“We are pleased that the number participating in the Memorial is so great, because it manifests much interest in the truth everywhere, and this is as it should be. The grand total reported to date is 90,434, which is 25,329 more than were reported a year ago.”
56
Truly the “slaves” of Christ, the class pictured by the slave entrusted with “five talents,” and the class pictured by the slave to whom two talents were committed, were prompt and early in ‘doing business’ with them, so as to add other areas that would be fruitful with more disciples of Christ. The published facts prove that these “slaves” were being blessed in their efforts and were rewarded with increase. This encouraged them on still more.