Back in the day, essentially _every_ version of Unix had its own flags and/or interpretation of flags. Delightful for shops that freely put an HP-UX next to a SunOS, with a little AIX and IRIX over there and a DYNIX in the backroom. You'd think that'd be rare, but it wasn't. "Open standards will make everything compatible and interoperable" had not yet quite been exposed as a deathtrap Big Lie. Universities, multi-nationals amalgamated by M&A, orgs that believed philosophically in mix-and-match... lot of places had to navigate "-r on systems A, C, and M. -R on B, D, and others by default."