If the main upgrade (M/MK) is in 1969, I think that Vietnamese, couldn't do anything to SR-71, and this damage is highly uncertain... With just 2 G's over 20 km, in "T/T" mode.... I am very sceptical it happens.

The mentioned date is the fielding in Hungary.
I have no info about what the Vietnamese got, and when.
(probably we got later than the Vietnamese)

Hpasp
Free SAM Simulator, "Realistic to the Switch"
(U-2 over Sverdlovsk, B-52's over Hanoi, F-4 Phantoms over the Sinai, F-16's and the F-117A Stealth bomber over the Balkans.)
http://sites.google.com/site/samsimulator1972/home

Book from the author - Soviet Nuclear Weapons in Hungary 1961-1991
https://sites.google.com/view/nuclear-weapons-in-hungary/
thumbsup