Question on Model Changes and Frequency

[HangOutdoors]

For my own edification, how often do they make minor model changes from year to year? Not the big redesigns. For example, what are the odds, without a major redesign, that Yamaha would filter down some of the 25' changes to the 21' line next year or the year after? Also, what is the potential in a year or two that Yamaha would make minor/major changes to the 25' model because of use case and other potential issues? Is it just customary to hold the model for years without minor changes?

I do know that they change colors and such every year, but I am wondering outside of that.