Master Gardener: When to pick avocados from the tree

Q: I have 3 avocado trees in close proximity to one another:  one Bacon, one Hass and one Pinkerton.  The Bacon and Pinkerton are approximately 5 years old and healthy; the Hass is relatively young. The issue is that the fruit from the Pinkerton, though large and profuse on the tree, never becomes “ready” to pick (darkened skin/texture, dark spot on the bottom, etc) and therefore never ripen (“in the bag’ method or otherwise) when picked. I have tried keeping th