A vexing issue. I think the Shakespeare entry in Fleisher is a good guide. I'm pretty sure Shakespeare's birth and death dates aren't listed in Superman #44, but there they are in the Encyclopedia!
To a certain extent, I wonder if we can assume (up to a point) that figures such as JLA members or their arch-nemesis are relatively well-known in Superman's world? Good question.
I guess this is another can of worms, but another guide would the entry in Fleisher for Batwoman, which gives a general overview, beginning with the date of her first adventure, and then notes a non-canonical source (Detective Comics 233) before going on to recount her "canonical" appearances in World's Finest, etc. I hesitate to mention it because a little bit of this goes a long way. These entries usually mention that the person is "famous" or "universally known" or something like that.
I don't think this is as important an issue as Earth-2 or the inclusion of post-Crisis issues.