How many times over the years do you think that someone has bred these two morphs together and then incorrectly sold the offspring as a Lesser when it was really a Butter? What if this happened near the beginning of these projects before they were widely available to the public? Because of this, perhaps a few dozen of the first "Lessers" were actually Butters, and now a large portion of the Lessers/Butters in the world could be incorrectly labeled.
It's a good thing that they're the same morph and it doesn't matter.