My guess would be that Victor Airways were defined with reference to a VOR radial. Over time the magnetic variation changes so although the 270R from VOR might still be the 270R from VOR, it might actually be 266M these days, bearing in mind these V airways may have been around for decades.
Otherwise you'd have to either re-do all the V airways on the chart or "rotate" every VOR with a Variation change....
Purely a guess though!