Complex sentence: Although Central African CFA francs and West African CFA francs have always been at parity and therefore the same monetary value against other currencies, they are separate currencies and could theoretically have different values from any moment if one of their monetary authorities decided it.
Split into simpler sentences: Although Central African CFA francs and West African CFA francs have always been at parity and have therefore always had the same monetary value against other currencies, they are in principle separate currencies. They could theoretically have different values from any moment if one of the two CFA monetary authorities decided it.