How can you assume he gets the big stuff right when the small stuff is wrong?
Here's my advice:
Don't "assume" that any writer ever gets the big stuff right.
Some do most of the time. Some do some of the time. Some do none of the time.
Some are smarter than others. Some are more careful than others.
Make your own judgments.
Over time, writers tend to reveal themselves -- as smart or not, careful or not.
I'm more or less with Brad Klein (and Ludwig Mies van der Rohe) on this one: "God is in the details." I find it very disturbing -- but not at all surprising, based on my experience with publishing-house so-called "editors" -- when I find a bunch of small errors in a book.
Even if Feinstein gets all of the big stuff right (and I haven't read the book, so I don't know -- and I'm not sure I'd know even if I did read it!), and even if none of the plethora of little errors changes the story "materially," the little errors are legitimately criticized, because they tend to undermine the whole effort ... the same way one bad hole, or a couple of Stupid Trees, or a few misplaced bunkers undermine an otherwise-admirable golf course.
Luckily for Feinstein, his errors are more easily (and much less expensively!) remedied than those of a golf-course architect.
It'll be interesting to see if the next printing, or the paperback edition, contains the same mistakes.