What an exciting development! I have not followed this phenomenon at all, and so haven´t encountered any literature that might directly try to explain it. The closest I may (?) have come is a report that asserted that the COVID virus seems to hijack (and thereby block) a particular site on the nicotinamide>NAD metabolic pathway, which assertion was then used to speculate that nicotine supplementation (via patch, gum, or lozenge) might dislodge (via replacement) virus particles from the hijacked site, restoring that site to normal function. (I think that this report is one of the bases for the growing popularity, among long-haulers, of nicotine ingestion/absorption (via lozenges, gums, patches) as a potentially viable COVID therapy.) Because my own understanding of the science at this level is limited, I can´t begin to even to guess intelligently how exposure to the COVID virus and Paxlovid would resolve pre-existing chronic disorders, but intuitively, I sense that the conditions in you that were resolved after COVID and Paxlovid might have involved metabolic pathway disturbances that were somehow corrected when/if the virus, and then the anti-viral, arrived on the scene. This scenario would suggest that the relevant pathways are still occupied by viral and/or anti-viral materials, and that all the while these materials have turned off the processes that were fueling your osteoporosis and arthritis, they are also causing unwanted long COVID symptoms. (Real scientists on this forum are surely cringing as they read this crude hypothesis, but at least this hypothesis may serve as a prompt for us to learn more about what the hoped-for correction via NAD therapy looks like at the cellular metabolic level.)