Ladies,
I must admit that I cringe when I read a thread title such as this, as it is difficult for me to imagine piece-mealing a guide in the way that you would have to do in order to cover two histories in one year.
I can understand that those of you who are sharing thoughts on this thread have children who are outside of the target age range of which our guides are typically designed, which places you in a unique category.

You each were so gracious in the way you shared your thoughts on this thread, and I really appreciate that! However, for our other board readers, I do want to clarify that it is truly far from the way I intended for the guides to be used to skip certain areas of the guide all year, or randomely complete some parts, or to combine multiple days of history readings and assignments into one day. This is because combining several day's work into one day is definitely a move toward the "cramming it in" philosophy of learning, which is a move away from the style of learning in which I write the guides. A more Charlotte Mason focus on fewer things of a higher quality done more slowly over time is our desire.
While you are the parent and are able to decide on the best education for your kiddos, I will caution that if you begin dropping too many things from the HOD guides and begin combining and condensing things as well, you will quickly come to a point where you are truly not really doing HOD any more. Instead, you'll find you are simply choosing from our guides like a buffet and losing the threads which run through each day and tie the various subjects together. By using a guide in this way, your child is also losing the balance that we so carefully plan within each day.
With this in mind, I would encourage anyone pondering using HOD as a "buffet" to rethink the way you are considering using HOD. I can understand using a 4 day a week guide, schooling 5 days a week instead, to hustle the pace in which the guide is completed. This still allows the guide to be used in its original form, doing a day within a day, but also allows the guide to be completed more quickly. This is the first way we would advocate hustling through a guide, if needed. We have done this ourselves.
If you have a high school student using a guide that is technically not targeted specifically for high school students, I can also understand having to enhance or substitute in the area of science. I can understand using different various language arts components (to a point) and understand choosing a different math (as long as it does not add too much time to the day).

However, beyond that... tweaking begins to upset the balance and the flow of the HOD guide. While, of course I may think this partly because I am the author, the other part of the equation to consider is that tweaking often results in the guide losing much of its skill-related teaching and cohesiveness whenever deleting and adding begins. It seems to me that once the tweaking begins, it is only a short time before the guide hardly resembles an HOD guide anymore.

Often the families for whom HOD just "doesn't seem to work" are those who have tweaked HOD to the point that it is truly not HOD anymore! I share this because I know I have done this myself... tweaking curriculums with my oldest son until they no longer resemble the program that I started with!
If you are to the point where you wish to do two HOD guides with one child in a year, then it is likely you may need to look at a different curriculum to meet your needs, as I would never advise that HOD be used in that capacity. I share that thought with much reluctance, as I would of course hope to have you continue using HOD. However, I also want HOD to be used successfully in the way in which it was intended, as each component of the guide has its purpose, place, and timing in the guide.
Hopefully, you will find when you come to this forum that there is continuity in the advice you receive from me.

This is because after over twenty years as a teacher (both in the public and the homeschool setting), I pretty much know what my philosophy is in each subject area, and this philosophy directs the design of our guides and how each subject is planned to be taught.

Since I am not continually flipping and changing my belief system from year-to-year, but rather fine-tuning instead, my advice will not continually be changing wildly from year-to-year either.
This does not mean that each family will not receive personalized advice on placement or personal help in making the guide work for their family. It just means that I still believe in the philosophy and design behind each of our guides from
Drawn into the Heart of Reading on up through the guide I'm writing now, and I still know the purpose behind each box in each guide (and the skills and learning that will be omitted when things are skipped)! This is why I just cannot advocate skipping, omitting, substituting, combining, and condensing your way through a guide. At HOD, I write the guides so that one guide is designed to truly prepare a child well for the next guide in line. However that will no longer be true, if families skip, omit, substitute and change their way through HOD.
You will know best what will fit your family, and I wish you the best in finding that fit. If you do choose to go the HOD route, I would love to help and encourage you to use the guides as closely to the way they were written as possible in order for you to get the full benefits of each area of the guide. If HOD is not a fit for you, you will know this too. I wish you the Lord's peace on your search.
Blessings,
Carrie