Yew can count on that Pat B, but there is a lot of good heartwood under the sap and outer rings in a decent Yew trunk so many good bows can be made from that with a decent backing.
I however, would consider rawhide as one of the lesser backing materials as it tends to deaden rather than improve the cast of a bow.
I have used sinew, Bamboo and Hickory as backing for inner heart Yew bows with good success. Often using a planer for a flat surface to allow a Bamboo or Hickory backing strip is fast and easy. A sinew backing on an inner heartwood bow that is also shaved down by growth ring is still probably the strongest and better performer - but it does take more time and careful work.
For sure the best ones come from the sap/heart combo, but that Yew wood is too precious to throw away if your stave/trunk is a good size one.