Can c-diff recovery peak and ebb? up to a year? felt normal-ish, but after series of colds, now feeling almost back to square one - nine months later

Yes: Need to follow up testing with your primary doctor as this could be a recurrence or stress from all your illnesses. Hope you feel better soon.

C.diff: Can be recurrent through multiple treatment rounds. And sometimes after an intestinal infection and treatment, it can take time for bowel habits to normally, but after nine month mark you really should start to see improvement. Nonetheless, you should review this with your healthcare providers, at least to readdress possible recurrent c.diff infection.

Probably yes: C. diff has very significant long term consequences. Even after an apparent cure a significant number of patients will relapse. Patients in support groups report ongoing feelings of ill health. Perhaps this is understandable given the severe derangement of the individuals intestinal biome and the increasing awareness that our very existence and health is dependent on our intestinal bacteria.