They do create a sort of schizoid split in Cap's continuity, though. When Steve originally returned in 1964, everyone clearly knew that he'd "died" in 1944 (or else, that he was gone). And that feeling's been acknowledged since. However, the retcon establishes that the government pulled the wool over everyone's eyes, and, at some point in the late 1940s, Jeffrey Mace simply retired, with Cap, as far as everyone knew, still alive.