Hi there. I've been through the very same issues. Pixel is now a year old and has returned to using the pee pads reliably. She was fantastic right up until she was spayed; she was sick from the anesthetic and had an allergic reaction to the pain meds, poor little soul. She had several accidents, so when she was feeling better, I steam cleaned the rugs. Mistake; she stopped using the pee pads entirely after that.
It took a few months to get her back to the reliable state again, but she's there. She has done a few other weird things (like ruffling up the blankets on my bed to make her "nest" and then peed in it!) but she's pretty good otherwise. She has missed the pee pad a few times; she thinks she's on it because her front paws are, but her hind quarters are dangling over the edge.
I finally clued in and bought a clear plastic rug protector and cut it to fit where the pee pad goes; this way, if she misses, the plastic protects the rug and it's very easy to clean up.