Maybe it's time for a lesson in bolt strength, lug torque, and wheel studs.
First of all, lug torque as specified by the manufacturer is a somewhat nebulous figure. It is frankly impossible to specify a torque for wheel nuts that will be consistent and applicable across the board for every application.
1) Factory specs assume new condition threads, without lubrication, on both the nut and stud. Any corrosion or contamination of the surface will increase the torque requirement, any lubrication will reduce the torque requirement.
2) Remember, tightness is not relevant. What is relevant is the stretch on the stud. The 100ftlb recommendation is only a guess based on a new stud/nut combination. It is possible to overstretch a stud with 90ftlbs if you use some lubricant on the threads. It is possible to under torque at 110lbs if the threads are damaged.
3) Stud stretch. An experienced hand will know when a stud starts to yield. Unfortunately for everyone else this may be hard to recognize. Once a stud has started to yield, it cannot be torqued. Period. It will not hold. You have to replace it. On a car 15yrs old, it is very likely to have fatigued studs.
4) All bolts have a life cycle. They can only be torqued to their proper stretch point so many times. Depending on the quality of the bolt/stud, this cycle is probably in the range of 8-12 times. After that the stud has to be replaced or it is not able to hold it's torque anymore. If you are a person who tends to over torque a bolt, or maybe the previous owner was, then lifespan can be seriously shortened. People who change tires/wheels at the race track should be especially aware of this.
5) Over-tightening of the lugs can ruin your aftermarket wheels, warp rotors, and cause highway speed vibrations.
6) Lubrication on the threads does not cause the lugs to back off. If the stud has and is holding proper tension, it will not back off. Think of all the bolts inside your motor. They are all fully lubricated before assembly, use no locking devices and they simply do not back off. Ever.
7) If a stud was torqued correctly and the nut comes loose then that is a huge red flag - you have fatigued studs! Replace them.
8) Nuts. Nuts don't stretch and so they aren't subject to cycling failure like the studs are, but the threads can become damaged. If the nuts do not go on easily by hand, they should be replaced. If the nuts feel loose when threading on by hand, they should be replaced. If the nuts have galling on the conical face, they should be replaced, but if they have galling on the face (much more common than you think!) then the wheels have also been damaged. Be aware of this. Again, for you track guys, using lug nuts with galled conical faces will damage your other wheels as well.
9) Within reason, no amount of driveline or engine torque will ever shear off any wheel stud. The studs do not carry a significant amount of rotational torque. Instead, the wheel lugs clamp the wheel to the hub and it's the friction of the wheel against the hub that carries the torque load of the driveline/motor.