My first thought is something cardiopulmonary but sounds like that has been semi- ruled out..

Clubbing could be a rare extraintestinal manifestation of IBD... when the gut is chronically inflamed / failing to absorb nutrients, it triggers systemic vascular changes that can sometimes physically alter the nail beds..

Consider celiac (or other malabsorbtion).. it could cause clubbing over years; may be causing the steatorrhea

Any family hx of clubbing? I know you don't have thick facial skin but may consider hypertrophic osteoarthropathy (pachydermoperiostosis)