Bale counter is usually connected to the linkage that you set the length of the bale with. As it goes though it's movement it activates the counter, so it counts each tie.
The items are the counter, bracket, arm on the counter, spring related to the counter.
I've never seen a counter connected to the knotter, only the trip arm. I've never seen a massey baler, only IH (too many years ago to remember), Deere and New Holland. All of the balers that had counters were similar to the set up in the picture.