I have been going through my adult Sunday School courses and have just finished revising and expanding the course on the book of Romans. I realized that some things that I would have included automatically while teaching the material were not actually written down, so I have incorporated these things and added further explanations, though the number of lessons and the material covered in each lesson remain the same.
For those who have used our Sunday School curriculum for high school students or adults, you should be aware of the books available on the Planters Press page. Many of these books are expanded versions of some of the courses in the curriculum:
Making Dry Bones Live is a detailed Church History text of which 9-12II2 is a condensation; I have also used the book for adult Sunday School, covering a chapter per week.
Thinking Inside the Box is a much more detailed version of the Christian Perspective course in the adult curriculum.
Eternal Values for a Valueless Age is a much more detailed version of the material that appears in various forms in 7-8II2, 9-12IV3, and the Ten Commandments adult course. I have also used this book for a much more thorough Christian Ethics course in adult Sunday School spread over three quarters.
The Bible Tells Me So is a much more detailed version of the material contained in the first quarter of each of the years of the high school curriculum. I have also taught each chapter as a separate course in adult Sunday School.
The benefit of these resources is that each one may be purchased for a significantly lower price than the quarters of curriculum despite the fact that they provide much more information in much greater depth. Please check them out to see if they can be of use as you instruct your congregation.