I do not know if it was betrayal, negligence or subterfuge that caused it to fall into Seelie hands. Until we know which other one is gone, I cannot rule out that the one we speak of may have found its way to Solais' hands. Though I fathom the Fox's daughter giving it over to them.

And for the answer to your question regarding the Seelie, that is a question better asked of the one that networked the whole endeavor. [In other words, ASK WAVER, as Saber doesn't know exact numbers.]