Surprisingly, yes, there IS a method to the madness.
The third letter designates how many slides a plan has. For instance, the D is double, T is triple and Q is quad. The second refers to the type of plan: A = atrium, etc. Unfortunately, I also have CRS and I forget the first letters' meaning.
But if one did remember them all, it would be easy to describe a floorplan from the letter-designation.