User blog comment:Pualover/Overlord Power Level/@comment-138.162.0.42-20150910182203/@comment-203.215.118.224-20150913103058

True. In vol 1 Ainz asked Sebas if there was any floating castle outside Nazarick. This floating castle could be the same floating castle of the Eight Greed Kings.

As for the WCI in Slane Theocracy:

"Now,  Her job was to protect the sanctuary where the five holy equipment were laid." ~Vol 4 Intermission

There's no indication that these items are WCI. It could be any Divine, Legendary or lower class equipment left by the Six Great Gods. They just deemed them as "holy" because it was "left by gods".