It’s annoying not to have to average publisher number for historical comparison, but the peak figure it still useful. It is more volatile than the average figure, but in the long term it evens out. So for any given year the average figure would be more acccurate to have, but in the long term the peak figure reveals the same trend.
To be clear JWs are doing much better than most churches. The latest Church of Scotland Yearbook has just been published for example. Get a load of this. Their latest membership figure is 337,000, which is down from 661,000 in 1997.
By contrast Jehovah’s Witnesses in Britain grew from 132,000 in 1997 to 139,000 in 2017.
So while the Church of Scotland declined by 49%(!) JWs continued to grow modestly and added 5%.
I don’t know of any other significant Christian denomination in the UK (apart from churches that comprise mostly immigrants) that has grown at all over the last 20 years.
I suspect that JWs will begin to decline in the UK, indeed the number of congregations has already begun to decline. But the fact remains that JWs have done incredibly well to defy the trend of secularisation in the UK up to now.