Sketches can be off, but not always. I watched a program on the Golden State Killer the other day and some of those early sketches were spot on. So I wouldn't put a lot of weight on the sketch, but I wouldn't just assume it isn't accurate either. As Shutter said, the three stews descriptions were pretty close and I'd put a lot of weight on those. Some suspects, and Kenny is a fine example of this, can be eliminated based on several different things.
As usual, I am full of questions!
1, Did anyone see Cooper through a plane window from the outside of the plane?
2. Did the official who went on the plane wanting to talk to Cooper get a glimpse of him?
3. Any witness reports from people waiting to board the plane with Cooper?
4. NWA counter descriptions where Cooper got the ticket?
5. Any tv footage of Cooper, even a glimpse?
6. Anyone get a glimpse of Cooper through their rifle scopes?
7. Were any security cameras filming the parking lot or inside the airport?
8. How large were his hands - any description of his hands/finger nails?
9. (nobody reported large ears in proportion to his head)
10. . . .