Just a last gasp: The source of a phase issue (one channel out of phase with the other), if there is a phase issue, need not be limited to the connections of the color-coded leads at the cartridge; it could be downstream at any junction. It could even be at the distal end of the very short leads between the cartridge and the headshell, if someone misconnected the leads to the pins on the headshell, for one channel. (This also assumes you use a tonearm with a removable headshell.) I realize you are now satisfied, but just sayin'...
It's not even out of the question that the defect in your cartridge, if there is one, is simply that connections to the external pins for one channel are reversed internally, although that would be hard to imagine for a company like AT.
I offer this only because I find it unlikely that maladjustment of azimuth or of VTA could have the particular effect you describe, unless azimuth was WAYYYY off, maybe.