The Classic 84 was originally a list of posture made famous by Bikram’s mentor, Bishnu Gosh, and was the foundation of his college of physical education. In the states and Bikram Yoga community it is referred to as being Bikrams advanced practice. The 26&2 in 90 minutes being Bikrams beginner yoga class.
You don’t need to be an “advanced” yogi to practice the 84! All it takes is faith, self control, willpower, concentration, and patience. You don’t need to do every posture, either! Most of the postures are part of mini-series within the class, so if you can’t move on to the next posture in a sequence, simply work a drill that will help you develop that skill or skip it and move on for the time being!