Storing butter for longer than a month I have had unsalted butter in the fridge for a while and used it from time to time. Now I realize that's it's been there for many, many months. It tastes fine but is it safe to keep it longer than a month?
Oxidation can make the fat in the butter rancid.  You would taste and smell that, so it's probably safe.  Refrigeration and darkness slow the process of oxidation.

I freeze butter and take it out of the freezer a stick at a time.  Butter appears to last approximately forever if frozen.