I was looking at the detailed units and they are identical for the first five and only have one additional topic for 6 through 8.
They two additional units say they cover ~30% of the material on the BC exam, so they appear to be more substantial than the other units. If the additional topics in the two enriched units are proportional, that’s another 10%.
Yes, I certainly wish our school had offered BC directly. I probably could have fought to have my daughter take it, but she would have had to learn AB in the first 4-6 weeks, alongside classmates that had a full year to learn it, and would have finished our school’s math sequence in 10th. We used AoPS, MIT OCW, and competitive math to enrich her math learning instead.