BM-21 Rocket Launcher question

What year was this truck-mounted rocket launcher first used by the NVA in the Vietnam War?

The Hobby Boss model has become available from my local retailer and I am sizing up my options...

cant find exact year mate at all first combat was the sino soviet in 1969 but for vietnam cant pin a year down.

SIPRI shows deliveries of 400 Type 63 107mm supplied 1965-1968 & 300 BM-21 122mm supplied 1969-71 with the note 'probably aid' on the latter.

from mark julian on red storm rising

Oh and 100 BM-14 140mm delivered 1965-1966 comment 'second-hand'.

I was reading accounts of the 1969 Sino-Soviet border conflict recently and came across the tidbit that the Soviet military leadership in the Far East sought authorisation from Brezhnev for use of the BM-21, which allegedly had been kept a secret despite having gone into Soviet service some six years earlier. Why it would be considered secret, anymore than previous Katyusha type systems beats me but if true, it suggests that the Soviets would not have been exporting them prior to that. Apparently it made a considerable impression upon the Chinese.

https://www.cna.org/archive/CNA_Files/pdf/d0022974.a2.pdf

Thanks guys - I actually forgot I sent this query.