A 25.5" scale shifted up a fret is 24.069", which is plenty close to 24. I've only measured the scale on one 24" Fender (a 66 Mustang), but I'm pretty sure that was the actual scale length. Nut to 12th fret was about 1/32 more than 12". So, they were probably using existing saw bars with the nut slot cutter moved to the first fret position. Edit: What Crazydave said.