Usually true, BUT the word "never" in calling coyotes, is never going to be true for all. Same as the word "always" because even though coyotes have strong tendacies to act certain ways, there will be those that don't read the same play book. I've seen coyotes that have gotten shot at, barked at by mouth, and they stopped only to get shot at again, and once again stopped because of yipping sounds or other sounds, and then get shot at again. I even witnessed a single coyote that got shot at 10 times before getting hit on the 11th shot, and it never fleed the area. Don't ask me why, but it happened, on film for those that doubt that statement.
As far as calling them in and shooting at them and missing, even then they can be called in again some day. Simply by sitting up in a different spot and using a different sound, they can be brought in some where down the road, weather it's a week later or a day later, it can be done.