Yes, you don't really need it.
It's kind of a legacy of our early prototypes, when the monster cards were sleeved and had no back, so a year marker was pretty useful by then.
No one (including us designers) noticed that with the big number on the back of the monster cards it was "redundant" to say the less.
You can use the marker as a replacement for some other game, at worst.
Thanks for your answer!