Beau,
In some cases it is true that the Yellow belt techniques are part of a larger technique at a higher level, but not always.
Belt systems, I believe, came about to show progress, and to collect fees.
In American Kenpo, there are approximately 154 techniques and then some extentions - depending on whose system you are observing. If a studio can test you 10 times (15 techniques per belt), they can collect 10 testing fees. And you will advance one belt level every four or five months (assuming one technique per week & a couple of weeks review). If however, the studio teaches a 24 technique system, there will only be 6 or 7 testing fees, and your belt progression will be slowed to perhaps every 7 to 8 months.
Different instructors have different methods of keeping students attending class and paying for knowledge.
My instructors' instructor tells me that in order to put on a black belt, a student should be proficient in those 154 (or so) techniques. He is less interested in how many colored belts I went through to get there.
Now, if you turn to the structure of Ed Parker's American Kenpo, as laid out in his Infinite Insights books, there is a reason why his techniques are broken out in the 24 technique per belt format. But, those reasons become less important once you achieve proficiency (black belt).
I would say that what is truly important, if your choice is to study American Kenpo, is that you find a competent teacher that can work with you through the complete system. In this way, you will gain not only knowledge of self-defense techniques, but you will also gain an understanding of the guiding rules and principles of motion that make up the system.
Good Luck.