Great question. Because the mods became so popular at the time, CAL ultimately offered an HDCD/PowerBoss model for sale with all the benefits up front. To your question about how do you tell? That can be deduced from wether or not the unit you have/want originated as a full featured ICON mkII HDCD/PowerBoss from CAL or if the unit had a mod/upgrade done to an original/older standard ICON after the fact.