Year 7 /26\ guns (1962) are certainly in the correct range for VN usage.
You more often find year 10, 11, 12, & 13 (1965, 1966, 1967, & 1968) guns as they were 'fresh' off the line and likely to be shipped out as direct clandestine aid to the PAVN (NVA & VC).
Ghost guns, letter series /26\, year 2 & 3 /26\, Romanian, and Yugoslavian VN bringbacks are few and far between. They exist (well maybe not a Yuogslavian bringback, I've honestly never seen one and debate exists as to whether Yugoslavia sent aid or not), but not many of them.