I have complement C3 n C4 deficient, ivr beem diagnosed with adult stills d. N fibro? Is deficiency in those to really rare?

Not simple. No association between still's & these complement deficiencies. C2 and c4 partial and complete defifiencies are not rare, affecting 1/200 people each. People with c2 and c4 deficiencies are more prone to diseases in the lupus family.C3 deficiencies are exceedingly rare and pose grave immune problems. The problem with low c2, c4, and c3 may reflect consumption of complement by vasculitis. Fms not!
Uncertain deficient. Usually deficiency is one or the other and not both. Complement deficiencies are rare. There are other issues that might be going on your rheumatologist has probably checked for acquired low c3 and c4 or even an overlap syndrome since low complements are not usually seen in still and not related to fibromyalgia which is not an autoimmune disease.