According to other contacts I have in Ireland, Mr. Hume's description of the Order's staffing situation ("... there are currently no specifically dedicated staff for the archives") actually means that the Archives has no staff at all. What work they are able to accomplish is done entirely by volunteers.
Also, I don't know if you've ever tried reading handwriting from the 17th century, but "categorising" what they're looking at is undoubtedly a challenge under any circumstance.
I've been hoping for 30 years that something like the paymaster's book would turn up. I shall try to be patient a while longer.