One of the more interesting in-progress language changes happening in English right now is the community-wide indecision over whether to say "a couple X" or "a couple of X".
Is "couple" an adjective or a noun? On the one hand, you would always say "a single fish"; clearly, "single" is an adjective here. But "a couple fish" sounds odd -- almost a Yiddishism: "You want drink a glass tea?" And you definitely wouldn't say "a quartet fish", right? Somewhere between 1 and 2, something... happens. (I'm guessing it happens somewhere around 1.41421356237, although the academic linguistics community is still debating exactly how many digits of precision people typically observe in daily speech. (Just kidding: it's the presence of the singular indefinite article "a", which while consistent with "single" being an adjective forces "couple" or anything of equal or higher grammatical number to be a noun.))
And then what do you do when you need to formulate it as part of a comparative? "I made a couple more changes to the document." Yiicckkk, please, no. Ok, then how about "She made a couple of more changes to the document?" Worse, or at least differently bad: the changes were not changes of the "more" kind, after all; they were changes of the usual kind, and she just added more of them!
I am forced to conclude that the truly correct formulation is the one that nobody would ever say: "She made a couple more of changes to the document."