Driveshaft length tolerances +/-?

not knowing how that 49" DS is being measured makes it tough to answer. is that total with the yoke? no yoke? the corrected length accounting for slipping the yoke back after it bottoms? and if so how much? i've had driveshaft builders say anywhere from 1/4" to 3/4" slip. i've had one that was off just over a 1/4" from what i wanted, and it turned out to be fine.
always ask your DS shop how they like it measured