The article on the history of encyclopedias has several typos in it, corrected in red ink. There are only four different types of corrections made. In order of first appearance, they are (1) capitalizing an incorrectly lowercase letter, (2) lowercasing an incorrectly capitalized letter, (3) deleting a letter and (4) inserting a letter.
Each edit inserts, deletes, or changes only one letter. If you take each edit type one at a time and look at the set of letters affected by that edit type in order, you find that edits of type (1) spell out ENTRY, (2) ON, (3) EZEKIEL, and (4) MPHAHLELE. So you look at the entry on Ezekiel Mphahlele.
What entry on Ezekiel Mphahlele? Well, the puzzle is full of clues that you want the Wikipedia entry. Wikipedia is notably an encyclopedia in which it's easy to correct typos (as per the body of the puzzle); and in fact the text of the article used in the puzzle is lifted almost verbatim from the Wikipedia article on encyclopedias as it was on 14 December 2005 (as noted).
So you go to the Wikipedia article on Ezekiel Mphahlele. The date "14 Dec 2005" suggests looking at the edit history for that article. In the edit history, you will see that on 14 Dec 2005 an edit was made to this article by someone with the username "EthanHunt", giving it the summary "answer". This edit consists of replacing an HTML comment with the text "Mrs. Plum". The answer to the puzzle is MRS. PLUM.
2006 MIT Mystery Hunt