That should be true when the chicks reach Tractor Supply, but it doesn't account for the possibility of the chicks getting mixed up at the store.The chicks at Tractor Supply are sexed by the hatchery so it's about the same accuracy as ordering from the hatchery directly.
Chicks can get mixed up by employees at the store, or sometimes chicks can mix themselves by getting out of one bin and into another. Some mixups would be obvious to anyone who knows anything about chickens (white vs. black chicks) and others are almost impossible to sort out until they grow for a while (White Leghorn vs. Cornish Cross, or pullet vs. cockerel of many breeds).
Ordering directly from the hatchery means that your chicks don't have a chance to mix with any other chicks after they are put in the box at the hatchery.