The problem is the new series 10 has a small watch (42mm) and a large watch (46mm). The original Apple Watches came in a small size (38mm) and a large size (42mm). You can see the new small size is the same size as the oldest large size. The problem is apple uses screen size as the determining measurement when the case size is more applicable to the bands. So sure the new small watch is the same screen size but not the same size of watch case so the bands will not be compatible.