Probably as with the 777, the first bird to get the new installation requires extensive certification, after which the conversion can be done at the pace of one each month.
Also, where did you see that? This is the first I'm hearing of it and there is no updated seat map on KLM.com.
Edit: I find an article on insideflyer.nl (
https://insideflyer.nl/world-busines...an-747-en-777/) that states in bold letters that the same seat is installed as on the B777/B747… and then shows pictures of a wildly different seat. To be fair that was somewhat expected as the BE/A Diamond Seat in the same configuration as on the B777 would be too wide.