One thought I do have is that there is a reason for repetition between sources and it's not so that what they miss from one source they might catch in the other! Encourage him to use the "repetition" to really compare and contrast. When details are different, are they important to the story? Are they the author's viewpoint or creative expression to make a good story? When they are about Biblical events are the details actually incorrect (when compared with the Biblical text) or are they just different interpretations? Do the differences or new details add to our understanding of the story itself, of God's work in the affairs of men, or of the culture and "feel" of the times?
Now, when they are still checking in with us for so much of the guide (or so little, compared to Preparing) is our chance to teach them to be like the Bereans, checking against scripture. While I can't decide for you whether he should switch guides, you can easily coach him to go deeper from what is already there.
As for switching guides, definitely call HOD. If you leave a message they will call you back and you can discuss the pros and cons of re-considering placement.
Just so you know. You're not the only one.

It took us 10 units before we realized that two of my kids were not going to grow into what was expected where I placed them and they both moved down a guide. It was the best decision ever. The relief was palpable when they could do what was expected of them in a day. We ended up with a 10yo in Bigger, a 12yo in Preparing and a 9yo in CTC. The oldest graduated after WG; the middle graduates next week after WH, and the third will graduate next year after a Canadian equivalent of US History 2, after 11th.
Blessings as you work through all the options,