I collect any variants that are recurring and involve a difference from the regular issued card. Probably most of what I collect would pass the 10 rule, a few not.
I tend to view a variation and a card intentionally changed by the manufacturer, but that would include intentional additions or subtractions from the card, clean up of printing errors, and DP differences. But it is virtually impossible to tell if a printing error was intentionally changed or just ran its course, so like most definitions it is often hard to apply.
And yes I know the hobby has haphazardly recognized many recurring unintentional print defects as variations. There are so many of them out there with 10 or more examples it would be hard to know where to start or how to
prioritize.. other than starting with the ones Greg has :-)