wow this guy has way too much time on his hands. All these numbers are practically useless after a team changes personnel. I don't think he takes that into consideration.
Drafthistory.com has O'Callaghan and Kaczur listed as Guards, not as tackles. So not really an error of omission on the part of the author, but an error on the part of the site the person compiled the information from.
Also of note, the Pats drafted Jeremy Mincey and Tully Banta-Cain, who were listed at DE's, but were going to be LBs for the Pats.