Personal challenge but is there one out there that you can claim if you have filled in your Cacher's name grid: 0 to 9 and A to Z?
It's one of the few grids I haven't completed. The other is the Placed Month of every year since May 2000; I've only found Jun & Dec in 2000 and not found one for Mar 2001.
The only similar challenge I know is this LC, which I think Neal has mentioned elsewhere. But I wouldn't be surprised if there were others out there.... (on various sites)