That said, the places where it has already been changed seem to be causing some confusion as "yearly" and "annual" actually do not mean the same thing in English for many speakers. (See the feature request for "Customize Membership card".)

Unfortunately, it does not seem to be stable—who considers "yearly" to be exclusively aligned with the calendar year (with "annual" meaning "renews each year on the same date, no matter what it is") and who considers "annual" to be exclusively aligned with the calendar year (with "yearly" meaning "renews each year on the same date, no matter what it is") appears to be a regionalism.

That said, it would be nice to be able to express the difference, but I don't expect that to be reasonably sane any time soon (in part because people often choose the one that sounds best instead of considering what it means in context in their region).