I have never paid attention to this detail either.
To add further to the confusion, 2 additional good pictures of 2 other watches:
- Close-up on the dial of my (ex) DSA, dated 1959 by JLC at the time (I wouldn't be 100% sure though, and I never looked at the dial backside to confirm):
No lume (or I don't really see it)
- Another DSA sold a few years ago by Dr Crott:
With lume
So, I am not sure I have really helped here