It is not really true that 3 COs are needed to make CG work, at least for most; more than one is usually just an individual choice.

The original book only says that the CO should contain 1) a mild surfactant (i.e., quaternary ammonium salts such as cetrimonium chloride), this is important as contrary to popular belief not all COs contain a surfactant and some may be better than others. 2) protein (but some prefer to avoid this), 3) emollients, and 4) humectants. So if the CO qualifies in all points it should be enough.

What may have initiated the trend towards several COs is the fact that many years ago a lot of people began with a pricey CO and in order to save money added a cheap one for co-washing, so a lot of newbies probably thought that was the way to do it. I myself used two to stretch my organic RO and eventually I didn't rinse it out at all so I would not waste it (and it did wonders for my hair that way!). Many people with healthy fine hair don't even need a LI, or like me most of the time, have enough with not completely rinsing out their RO.

So, if you have a quality and complete CO see first how you do with that one alone, the whole point of CG is to simplify one's hair care routine and narrow down the products to 2 if possible (a CO & a gel). However, those that manufacture curly hair products will encourage people to use more... and some PJs end up collecting a gazillion bottles and jars in their unrealistic hope that a "miracle" formula is going to even change their hair type...