Driving east toward Tupelo earlier today, I noticed US 278 had been realigned a lot around Pontotoc and again east to US 45 in Tupelo, from my car's nav system (which I keep with its original ~2007 data, to help me spot realigns). The HB reflects the first realign, but not the second, which moves the route's junction with US 45 south by two interchanges.
I'll be claiming US 278 mileage in MS west of US 45, in my next list file update. That will reflect my travels on the new alignment, since I never traveled the old alignments.