"lowly stackers manage to read the tins well enough to issue the correct stuff"
Actually, they didn't.
They entered the stock number into their inventory computer (if it wasn't an electronically-generated request in the first place), went to the location shown, zapped the can with a bar-codereader to verify it (something the line hogs don't have) and sent it out if the light turned green.
That is, if their warehouse wasn't one of the fancy ones like the USAF has where punching the number in results in a robot getting the tin and dropping it into the shipping box without the supply puke even getting out of his chair.