Been doing clocks now for over 30 yrs. I have never heard in all those years about the pendulum info being stamped on the clock movement for case makers but that is not to say that isn't what it was for.
I know on the Hermle movements that the number above the line is the pendulum length and the number below the line is the beats per minute. I have been told that the measurement for a pendulum is from the suspension post to the bottom of the pendulum bob and also from the suspension post to the center of the pendulum bob. A quote from one of my clock books says, "As seen in this diagram, the length of the pendulum is measured from the pendulum's point of suspension to the center of mass of its bob." IMHO that is just a starting point and I generally measure to the middle of the pendulum. Once I have a starting point then I put a optical sensor on my microset timer and time the movement out.