The 18th edition was the first edition to add some prefix differentiation to the price guide for the '37 series, so it may take a few editions for the pricing panel to get a real handle on what these notes sell for in the real market. As discussed many times in the past the pricing panel must be careful. The fact that you and I may pay a 60% premium for a G-T $10 Z/D because we are anxiously trying to fill a hole in our collection, does not mean the catalogue price is unjustifiably low. One we have purchased the notes for our collection, and if the niche is small, then there may not be a significant demand in the market to keep the price at that level.
/me