Expertise isn’t like pornography. You can quantify it, and often you don’t know it when you see it. There are several modes: There’s knowing the big, significant things in your field (stylistic differences between Weimar-Classicism-Goethe and Sturm-und-Drang-Goethe). There’s knowing the small but significant things in your field, like why it’s important that Gretchen says to Faust Bin weder Fräulein, weder schön/kann ungeleitet nach hause gehn. There are also small, less-significant things, details that can be corrected with a trip through the spell-check or a visit to Dr. Wikipedia: the spelling of Backpfeifengesicht; the precise wording of remark seven of the Tractatus Logico-philosopicus; the date of a writer’s death.
Awl columnist Rebecca Schuman has an entertaining piece on LitHub about the grave (HA HA you will get this when you read the piece) mistake she made in her (excellent) book, and the post has a very clever footer.