A claimant is often unsure of whether a medical condition is resulting from a new set of factual circumstances or a natural progression of the injury or disease. The doctor is concerned with treating the medical condition. OWCP is concerned with what is causing the condition.
I recommend that a claimant file both a new CA-1 or CA-2 or CA-2A. There is nothing wrong with redundancy. The exact form needed can always be litigated once all the medical is available.
Do not be concerned with multiple filings – the claims can always be combined.