I don't think Apple had one. People were using various third-party packages. I'm sure a lot of people had to migrate those.
Okay, so MS is the bad guy because back in '92 they didn't write their calendaring system to a standard that wasn't going to exist for another 5-6 years. Apple is a better software company because they didn't even have one until after the standard was published, but they wrote theirs to conform to it.