I understand specific labs are not entirely specific to certain autoimmune diseases, and its based off of labs and symptoms. but can anyone please explain the difference between mixed connective tissue disease vs. other autoimmune diseases?

There is a blood test called antiRNP titer which must exceed a certain high level along with presence of at least 3 out of several clinical features such as Raynauds phenomenon, scarring of of finger tips, hand swelling,inflammatory. muscle changes on biopsy,inflammation of joint linings for example. Lupus, rheumatoid arthritis, scleroderma wouldn't fulfill enough of these criteria.