Since 1993, I've owned a handful of Galaxy Radios and have never had one drift on SSB. It must be something that affects the newer models only OR, there could just be non owners who don't really know for certain and are just rehashing stories they've heard, making it seem like there are thousands of drifting Galaxy sideband radios out there racking up the QSO's.
What drifting I've heard of is happening while it warms up for about fifteen mins after being turned on but like I said, I've never actually experienced any of this with my mobile rigs not even during warm up in Dec, or January around SC.