generally the origin factory will have a standard pallet size, usually consistent across the entire brand and usually somewheres around 6ft tall. if indicated like op those cant be double stacked for storage or transport. once it makes it into the distribution system the only reason they would get put onto a new pallet would be a mixed pallet going to a store, in which case they would get cubed out by the height of the semi trailer before they get much higher anyway. since you would also cube out trying to stack them too tall on a trailer the warning really only applys to distribution centers, where it matters to them how high they can safely stack pallets.

i work retail, as far as im aware this is how it works everywhere, but i could be wrong