I have tested your Excel spredsheet for calibrating the axis.
I'm using EstlCam to control my X-Carve and the normal settings is like this:
When measuring the Y-axis over 200mm, I found the travel to be 201mm, (0,5%), so when this is entered into Excel I'll get:
This cange from 40 to 39,8 steps/mm actually incrised the distance even more.
I tried this formula in stead:
This decreased the distance very close to 200mm.
I have now tuned the steps/mm in EstlCam even more and now it is very close: