How much do you actually learn from the book Modern Chess Openings by Nick de Firmian? How much theory does the book actually cover and how far in terms of opening knowledge and building my opening repertoire will memorising every line of the book get me?
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how far in terms of opening knowledge and building my opening
repertoire will memorising every line of the book get me?

You will be an expert in historical opening lines, but you will understand nothing.
MCO, latest edition 2008 as far as I know, is mostly composed of chess lines with minimal notation. Each line usually finishes with an evaluation like &quot;=&quot;, &quot;+=&quot;, &quot;-+&quot;, etc.
I have the 11th edition from somewhere round about 1970. The last time I looked up a line in it was sometime in the 1970's. The main reason I still have it is that it is where I keep my signed scoresheet of my 1972 draw with Victor Kortchnoi - in a simul, obviously.
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