Wayne Bingham asked: Can anyone verify the year for the first DA side-pull calipers?
1973. From the book "the history of shimano" c 1975:
"in 1972, the dura ace division was organized in order to perfect the skill necessary to produce components of unmatched excellence"
followed by pictures from the 1973 catalog
Flandria was sponsored by Shimano in 1973, and won the "world cup" that year for best team.
I have seen even older center pull brakes marked "dura ace" too, but they don't appear in any catalogs I have (73,74,77)