If it seems they had "lost" your disc temporarily, I would check the report on it yourself. When they "found" it, they might have "found" someone else's.
It happens a lot more than you'd think. I had a big name dr at a big name place mix someone else's disc in with mine, and plan his treatment for me based on a problem I didn't have. I had an orthopedic doctor come back into the room after looking at my report and disc, and tell me my knee was completely shot with arthritis, cartilage gone, nada left, in places, so when I was old enough I would need a replacement, but until then, oh well, so sorry, nothing to be done. But when I got a copy of his report, he said only some mild cartilage damage (confirmed by a better doctor later on). All I can figure is some poor woman in the room next to me got told she was fixable with a little physical therapy, when in fact that could only do her harm and she had replacement surgery in her future. I had a neuro-ophthalmologist once leave me sitting alone in a room for nearly an hour (after 3 hours of testing), a nurse found me and thought the doc had been talking to me already, so sent him in where I got about 3 minutes summary and sent on my way. When I got a copy of his report a week later, there was an extensive paragraph detailing an extensive discussion we evidently had, only he never had it with me (in fact, that paragraph was in a different size and font and print darkness and margins than the rest of the document, and literally looked like it had been cut out and taped in from something else before being run through the copier), guessing he may have had it with another patient (or maybe he was just napping for that hour...)
These are just some highlights on mix-ups I have encountered. They happen way more often than you'd think. So check up on your missing ribs. Someone, either this time or on your previous x-rays, has screwed up.
(Either that, or figure out how you did it, you might just have the cure for rib resections--make them vanish instead!