An arrow's known spine only gets you in the ballpark. After that, there are many variables to achieve good arrow flight. Shaft length, point weight, feather style, string material, etc...
Proper arrow spine is more critical the less center shot a bow is. I find I have to drop a spine value for most of my longbows without a cut in arrow shelf. With a true center shot recurve, exact arrow spine is less critical. A very common misconception regarding traditional archery is, that little or no bow/arrow tuning is required. Not true! Once you have a bow/arrow combo that is properly tuned, the impossible is possible. Ask Byron Ferguson.