The problem isn't the side with the markings that start at "0" by the T and end at 47 7/8", it's the side with the markings that start at "0" at the end away from the T and end at 48" at the T. That first 1" marking, (which is directly opposite the 47" marking) isn't at 1" from the end, so none of markings on that side are accurate.
Now, I know that a Drywall T Square is not meant to be a precision measurement device and I know how to "shift an inch" to compensate for the incorrect marking, but I wonder why they bother to mark the inaccurate side in the first place. If you want markings on both sides, just start both sides at "0" by the T so that the markings line up and are accurate.
Seems like they could just make the T squares a true 48" and eliminate the problem. Maybe they do...both of mine were bought at the borg but they were bought 20 years apart, so it's not a new issue.
Oh well, such is life.