A has been consistently improving it since before the change, so it's only possible that they are managing to the metric if they had earlier access to it.

B may be doing that, but the graph doesn't actually measure how many bugs you closed. Those ones seem to have decided to manage by the metric, removing the variance but targeting a high, comfortable level.

Agreed on C, they did a large "hey, we will be measured by that now" one time effort and then forgot about the metric.

The change didn't improve anybody's performance.