You tell us your special dates and may forget about’em.
We remember them and will email you when their special antiversary approaches. A couple of times, at that, in case you need that (as do the founders here :).
Special antiversaries include 100, 500, 1000, 1500, 2000, …, 40000 days, as well as 500, 1000, …, 5000 weeks. That’s around a century, so should suffice 🙂