I am a Patreon of James’s at his podcast (wehaveways), which is excellent btw. I don’t doubt he’s made the odd mistake in his books and the negative G one above sounds a bit of a howler, but as someone who put his daughter’s birth month down on his sons passport, I understand how easy it is to make silly mistakes.
I find him to be a very modest, friendly, passionate about WW2 and extremely knowledgeable chap. Why not give his book a try when it comes out before making your mind up
?