There is a long tradition in pottery of changing the marking to reflect the year, just as there is in the production of silver plate. Which IS sort of fun. However, it drives the collectors rather nuts because you need to either memorize the markings, or carry around the key. (Has anyone else read the incredible book "The Arcanum" by Janet Gleeson?)
I was being a little tongue in cheek there, because bonsai pots really don't get sold as collectibles nearly as much as other pottery. And they usually aren't collected for their age, or rather I should say for the stage that the potter was in at the time. ("This is an early Stone Monkey, and this is from his red reduction phase") People may appreciate the potter, but they mostly buy the pot because they like it, not because it fits into a larger collection. (Hard to describe the differences in collecting... am I being clear enough?) They don't care about the year except as a curiosity perhaps. Whereas with some collectibles, a collector wants one of each type from each maker that they collect. And the earlier work is usually more highly prized, even though the later work may be more mature and refined. Go figure!!
Joanie