i would agree with paul/@pdreher -- in my experience as well, the 40.1 to 40.2 update was a substantive change, much moreso than the ones after the 40.2 (which are largely cosmetic and marketing driven, imo, with trivial sonic impact...)
i think the t-a-s review of the 40.2 from 2017 is illuminating with its in-depth interview with alan shaw -- worth a read
https://www.theabsolutesound.com/articles/harbeth-monitor-402-loudspeaker/