Here in the UK , STM came out on VHS in 1981.
SII followed in 1982.
In the US , my understanding is that STM came out in late 79' early 1980.
SII came out in 82'.
They then re-released STM on VHS in 83' to coincide with the laserdisc releases.
And that may jive with your experience of finding STM in 83' on VHS.
I have acquired all of them on ebay
Here in Cambridge, in the early 80s, we used to have a video shop which had TVs hooked up to VHS players positioned strategically at the front window, to allow people from the outside to look in.
One of my fondest memories(circa early 1982) is recalling the crowds that would form outside the video shop to watch STM on one TV and SII(simultaneously on the other)!.
Getting crowds like that that would never happen now!
But back then, to even get a glimpse of prestigious movies like STM & SII was like gold dust.......because you had to wait until they were shown on TV broadcasts.....which could place take several years after the theatrical release.