From 16 to 18 to 19*
Here's the match that probably led to the extra nerf: https://m.youtube.com/watch?v=wRMQjx3DePo
We'd never nerf or buff anything based on a single match. The Churchill Mk.VII was planned to become 19 popcap because spamming ~3 Churchills in teamgames (so with AT/TD support from teammates) was easy to execute and nearly unstoppable because of the immense HP pool and the lack of Axis non doctrinal units equipped to properly deal with it. It was changed to 18 initially as a precaution but then ultimately it was changed to 19 as originally planned. 19 popcap was supposed to keep an effective army composition (1 Churchill or 2 max, supported by a Firefly or ATGs) a viable strategy while discouraging full on Churchill spam.
That particular match only proved the point, but it wasn't the cause.