Well, the truth is, there aren't any varieties of avocados.

In order to get a Hass Avocado, you have to graft a Hass Avocado limb to some other avocado root. So, a Hass Avocado isn't a variety, they are all fruit off of the same tree grafted onto many roots.

Avocados do not breed true. Every avocado has a mother and a father. And that produces a unique avocado for every single tree.

The guy who bread Hass Avocados was known to go around planting avocado seeds (in other people's back yards) to see what they would grow.