Hello Bibi,
When zoom-lens is set to the intermediate focal length position, it may change slightly due to the camera shake, but the EXIF metadata will contain the same values due to the rounding to 0.1 mm or even to 1 mm. It means that practically two images are captured with the different focal length, but would be put to the same calibration group according to the EXIF information.
In case zoom-lens is used it may be reasonable to split the camera calibration group, if the alignment result is inaccurate.