Well let's see, where do I start. Since no one knows the history of the clock spring let's start with moisture. How many cars do you see in a salvage yard with the windows down? Can you be 100% positive there is no corrosion inside the spring? Since it's somewhat sealed the only way to know for sure is to pop it open and then it's junk.
From there let's say the entire column was pulled by the yard and put on a shelf. The clock spring is designed to have approximately 3-4 turns from lock to lock. When the shaft was pulled did the 17 year old kid turn the wheel 4 1/2 times? Maybe the coil didn't break but did it stretch enough that now a horn power feed as touching the power to the airbag ignighter?
That air bag is a hell of a lot more expensive than that clock spring. The collision industry is a billion dollar industry and insurance companies look for any possible way to save money on repairs since they are writing checked just about every second of the day. If they can save $$$ on anything trust me they will. They won't use any used airbags or any component.
Last but not least as a Technical Trainer for a collision company that repairs about 38,000 cars a month, yes 38,000 a month, I see many cars that the OEM comes out to investigate because the car was in a collision and the bags didn't deploy when they should have and someone was either killed or severely injured because of it. Is the used clock spring coming off a car the bags should have deployed on? Can anyone say that for sure?
I don't know about you but all the money most of us spend on these things an extra $100.00 or so to have peace of mind that that bag is going to go off when it's supposed to is worth it. Or better yet, that is doesn't go off when it's NOT supposed to.