35mm was the norm up until the early/mid 90s when the switch to 6x7 was mostly made. My father was shooting editorial and covers from the 70s through the 2000's and always shot a mixture of 6x6, 6x7, and 35mm the entire time. Although from 1998-2004 it was mostly 6x7 in RZ67 Pro IIs, and almost always Portra 400NC or 160NC.