Update: All 1944 blades that I have photos for (5 of eight) have the large Saka stamp on the nakago face.  The only 2 dated blades I have with the Saka + number on the mune are both in 1943, a Sadakatsu and a Zuiho.  All 8 Nagamitsu blades with the Saka + number on the mune are undated