[Nerwen]

So–

Both parties are rulers (whether literal or metaphorical remains to be seen).

Both have something in common.

They are not contemporaries.

"A"
–is "bold" (may or may not be significant).
–is associated with gold in some way.
–is long since dead.
–his/her/its enemies and realm are unknown. This may mean Legate wants us to guess, or it may mean all this has "now" been forgotten.
Very little information about "A", really.

"B"
–was around long before "A".
–was involved in nocturnal battles involving spears; something about this is what A and B have in common.
–his/her/its throne is "in cold, dark and stone". I'm not sure what that means– maybe just that "B's realm is now abandoned. But could mean "subterranean".
–ultimate fate was a "black pit". (Moria? Or does it mean "died in a dungeon" or something similar?)

Interestingly, it seems there are three distinct "bands" of time referred to– the "present", the past ("A"'s time) and the deeper past ("B's" time). If the "present" is the real present, "A" having died "long ago" doesn't rule anyone out, and is basically meaningless. If, however, it refers to some time actually written about by Tolkien– most likely the late Third Age, then it does narrow it down– for instance, "A" then could not be Theoden.