Rebecca,
As I'm thinking through your situation, I'm thinking you must be looking at this plan if you just continued on as you are:
CTC - Grade 6
RTR - Grade 7
Rev2Rev - Grade 8
Modern - Grade 9
Geography - Grade 10
World - Grade 11
American to 1900/Government - Grade 12
If so, then your son would miss the final guide in the cycle but would have covered that material in grade 9. He would miss the Economics/ Personal Finance part, which would need to either be added to Grade 9 or added to a different year.
As far as what your umbrella school allows, it is likely that you could still folllow the path above, but you will have an additional credit in the History area beyond what they require. It is usually fine to list an additional credit, as it just falls under the elective category then, if it was earned. Typically, the listed requirements are minimums. So, if you followed the schedule above your son would end up with a credit for Geography, a credit for World, a credit for American, and .5 up to a full credit for Government, and .5 for Economics/Personal Finance. Typically, not more than 4 credits are given for work in the "History area".
You could have a different situation, but what I noted above is often the case.
Blessings,
Carrie