There has only been 1 6055, however, like all of our products they are constantly refined and updated but here is a breakdown. Note the July revision is not so much a revision as what was already planned, we released some early (fewer than 200 worldwide, only about 50 came to the US) with an older shaft we had in stock, due to impatient customers with pre release orders.
Introduced June 2007
Revised July 2007 for 316 shaft to 316TI shaft
Revised Oct 2007 with new Luran plastic clamp
Revised January 2008 to thicker 6025.740 black plastic disk and tighter fitting propeller on shaft
Revised Oct 2010 with new silence clamp and 6055.740 anti attenuation disk and blue propeller blade (cosmetic change)