I don't have a book about counterstamps and was wondering if anyone could share any information on this counterstamp, like the rarity or is it a better stamp or anything?
Neither counterstamp is listed in Brunk. That in itself means little as far as value goes - it simply means that the names hadn't been reported to Brunk. Research that definitely ties either name to a location, occupation or notoriety of the person is what will add value to the piece.
That said, it's a nice piece on a solid coin. Double or multiple c/s are not that unusual, especially on larger silver. Neither name is that distinctive but having both initials on both names gives you a fighting chance in the research battle.
Not to say it's the same gent, but R .(Robert) F. Adair was a noted jeweler and manufacturer in Maysville KY c 1850/1860. If it's his retail countermark used on bought-in goods, it would be desirable to southern silver collectors. I have not found anything about a W. R. Bagley.
Sorry for the crap image, but it's all I had on file (a surprise in itself)