Just because I have some calcium deposits on the skin, it doesn't necessarily mean I have Scleroderma...or does it? They're not clusters.

It does not. You are right. There is a clear set of criteria to confirm the diagnosis of scleroderma. Until then is only suspected/ possible/ likely. A rheumatologist should be able to confirm or rule it out based on symptoms, history, physical exam and review of diagnostic data.