There were many 'traditions' when cards were the primary input. Most languages allowed a comment/sequence number in columns 73-80. Before revision control systems, it was common to put the program/step/phase name and version on there, thus the few incremental numbers. Or number all the cards in increments of 10 - so a sorter could put a dropped deck back in order - the multiple of 10 was to allow for inserting cards later -- jeff jonas who still has a "numbering machine" stamper, just in case