Less cold hardy is relative. The Mexicola while considered cold hardy, is still less cold hardy compared to Duke or Aravaipa.
The West Sacramento Hass is cold hardier than a regular Hass and it is my least cold hardy avocado on my tree.
I got the West Sacramento Hass from a friend who planted a Hass avocado in West Sacramento. The tree died down after an Arctic blast when we got 12F. He cut down the dead tree and then the stump sprouted a tree. It grew quickly and survived subsequent cold of 22F-24F and bore Hass fruits every year. It must have undergone epigenetic changes and the cold hardiness genes were expressed. It suffers minor leaf damage each winter.
The Aravaipa is the cold hardiest one that I’ve got. It keeps on growing even during the winter. It tries to take over the whole tree.