In the modeling world, HA and HC are interchangeable. It is a way to identify the initial batch of M1A1s from subsequent variants that had depleted uranium armor added during manufacturing.
M1A1"HA/HC" tanks were around prior to the first (Desert Storm) Gulf War. We had them in Germany as far back as 1989. Your above statement solidifies my opinion that you may have some peripheral knowledge from your dad, but a little knowledge tends to lead one to make wrong assumptions.
I didn’t mention the M1A1D since the discussion was about the use of HA or HC, so according to the model manufacturer’s nomenclature you use, shouldn’t it be M1A1HAD since the M1A1D are digitally modified heavies? [;)]