Wonderful example. For several years I taught at a convention where we used (in each class or event) the same model machine and the appropriate 1/4" foot that came with the machine and the same 1/4" button on the machine. None adjusted the same. We spent time at the beginning of the class calibrating the stitch width. So....proved that all machines and feet were not the same.
Therefore, some rules (if I can use that term) Always calibrate or adjust your seam allowance before beginning the sewing and make a test piece to be sure and then USE THE SAME machine for the entire project and never assume the measurement will continue throughout the projejct. For accurate work it is necessary to check and correct as the project goes along.
I took a class with Sally Collins recently. She is consider to be the master of accurate minitiature piecing. She said that the work is only as good as the last seam sewed. So make a section and then measure it and correct if necessary.