When I started working on the calipers, it was my first time doing so. In addition, it was the first time I had ever bled brakes on a car. The rear calipers on my car had three bleeders, one on the front side of the caliper towards the back of the car, one on the outside of the caliper on the front side of the car and one on the inside of the caliper on the front side of the car.
When I read the instruction on how to bleed the brakes, it referred to the inside and the outside bleeders but that was it. When I bled the brakes the first time, I took that to mean the inside (towards front of car) bleeder and then the outside (front of car) bleeder. When I bought the rebuilt bleeder, it only had two bleeder screws on it. One located on the outside of the caliper on the front side of the car and one on the outside caliper located near the back of the car (you can see them on the picture above).
There was no bleeder on the inside of the caliper. After a bit of research, I realized that the only two bleeders that matter are on the outside of the caliper. The third bleeder is the result of a re-builder that did not plug the hole but rather used a bleeder screw to do that. This made total since and once I realized it, made the job of bleeding the brakes earlier.
Consider this your public service announcement.