As far as is known for now, the sequence used on the 1954 early specials seems to be running off Manhattan numbers; from a trim standpoint, these cars are done as if they were 1953 Manhattans with 1954 tail lights and front sheet metal. When the regular Specials (3-piece rear window setup, 1954 Manhattan type interior and dashboard, etc) came out in the summer of 1954 (the Trade Letter announcing these cars--and at the same price as the early Special version--is dated in July) they continued to run the sequence.
Only the prefix was changed.