1) World's memory is far more poetic than Archive of silvery depths
2) "Archive of silvery depths" clearly lack ambition
As the one who came up with the name, I feel the need to defend it. The commonly used Reikspiel name I intend for the library is "The Library of Karak-Eight-Peaks". This isn't particularly poetic, but I think that it has its own charm in the form of being direct and understated - I'm going for a "Library of Alexandria" effect here, with the Library becoming so renowned that it makes the name "Karak-Eight-Peaks" synonymous with knowledge in and of itself.
The wordplay comes in with the Khazalid - the true name of Karak-Eight-Peaks, to the dwarves, is
Vala-Azril-Ungol: "The Queen of the Silvery Depths". The titular "silvery depths" are the gromril veins in K8P that the ancestor gods personally discovered and mined out (which Johann saw).
As such, the most proper translation into Khazalid for "The Library of Karak-Eight-Peaks" is "Kron-Azril-Ungol" - literally, "The Archive of the Silvery Depths". But because of the way Khazalid works, this also has a metaphorical meaning attached to it - the Library that is as the Silvery Depths were - ergo, the Library that
is a legendary deed, the library that
records legendary deeds, the library that is as gromril is, enduring and forever.
And yes, there is
Word of Boney that these meanings actually exist.