N-Deklination von Namen in Genitive Singular

Question

I am studying B2 grammar. In the book I am using (I don't know if I should name the actual book here) there is a bullet-point which reads:

Name und Buchstabe gehören zur n-Delination, bekommen aber in Genitiv Singular zusätlich zur Endung -en ein -s.

Then there are some questions. The answer to most questions follow that rule, for example:

Kennst Du die Bedeutung des Familiennamens Müller?

But this one doesn't:

Der Hof eines Bauern heißt Bauernhof

Why not? And are there many exceptions to the rule given in the textbook? In other words is it a valid rule?

Answer 1

The nouns Name und Buchstabe appear nowhere in the sentence:

Der Hof eines Bauern heißt Bauernhof.

Therefore, the rule you quoted doesn't apply.