I tried everything I could think... peeling by hand, cutting narrow strips first, beating on it with the head of the ax, prying it with the ax blade, and prying it with the drawknife wedged between bark and wood, etc. Nothing, it was stuck.
Did some reading about tree grafting and it explained that strength of the bond between bark and wood was related directly to cell growth rate. So fast growth rate means weak bond. Spring and early summer is high growth rate, so easy bark slipping. It also mentioned that the cellular growth rate is related to moisture... so dry weather when the plants become more dormant means tight bark... as Blackhawk mentioned.
So I guess slower growth late summer combined with hot & dry weather, combined with the tree location, etc. increased my work load and kept me from harvesting inner bark.
I did cut this tree more to try to get some inner bark to play with, and getting staves was just a secondary purpose. At least I got some staves!
Thanks for all the input.