Finally another sibley archive fan!! Brother! Seriously those people are saints for their I ongoin ef fort to digitize their holding(s)! I think we have a holiday dedicated to their existence over at pphilia. Or at least we should.:: 
Hi visitor,
yes,

- but until today I neither had known about the "two" resources, I accidentally surfed, and detected, as you can see, the link given above. Now, I checked the "direct" Sibley Music Library catalog, too ( it looks a little different, but I didn't compare the results of both of them..

).
They, all in all, look like usable and good info-resources (for "normal" investigations). The only thing I remember, is, that some IMSLP-files of various composers are classified by "uploader: Sibley" or sth. like that.
Nevertheless: A good info-resource, it seems.

Cordially, 8_octaves!