I really think the 'missing' year is just because of the way she writes her guides...with age ranges.
LHTH is 2-5,
LHFHG 5-7,
BLHFHG 6-8,
PHFHG 8-10...this allow us as parents to find the perect fit for
our children. We don't have to go with a particular grade level, and I love that! It also allows me to combine my dc using the available extension packs with
Bigger...and I wouldn't be able to do that with most other publishers' guides.

For us, my daughter will be able to complete the whole cycle, becase we completed
Beyond... in 2nd grade...and will just move through them from there each year. My oldest ds will actually miss out on the last of the 4-year cycle...unless Carrie decides to have extension packs for older kids with that guide.

(hint, hint) He may join in on the readings even if he's doing something else as his core for 9th grade. As for my 5 yo, we are using LHTH for his K'er year, which will allow him to complete all the manuals by the end of 8th grade as well. And our littlest, who's not even here yet, will likely follow the same plan as my younger two. However, by the time he/she gets to K...all the others will either be independent or semi-independent, so I might be able to spend more time with him/her like I could with our first.

(I love that I am able to plan that far..it's so awesome!)
I agree with pp's...you can choose to fill in the gap with other studies. Spend a year studying the various states, the presidents and first ladies, scientists from each state you study (and their inventions or contributions to society), add in composers and artists from those states, some poets for copywork...you could follow the last guide, but substitute the higher levels and such for each subject, KWIM? There are all sorts of lapbooks and free notebooking pages, etc. online. You could choose any topic you think appropriate or that your child wants to learn about, and just dig in. I'm getting excited about this, and I don't even have an 'extra' year to fill!
Anyway, that's my 2 cents worth. Maybe you can get something valuable out of it. If not, that's okay too. I'm glad you asked the question, because it's been fun reading what others have to suggest.