Anyone with access to loads of yew wood with note the differences in quality, and in my experiences elevation isn’t the whole story, and a lot of the best yew I’ve cut has been lower elevation, in very shady mossy lush forests. Sometimes even 2 staves from the same log will have slight differences, sometimes big differences.
When you rasp a piece of yew, the density becomes very apparent. I love a solid, dense, heavy, dark stave, but dimensionally they get quite small if your making a bow less than 40#.
At the end of the day, you never know what you have until your bending it. I’ve made yew bows from staves at sea level in full sunlight and they were great.
Even in yew country, if I find 50 trees, I might cut 2 or 3.