Originally, I had 1991 as the year of release for the Constructicons (from Rob Jung's list that he maintained back in the day) when I kept track of my stuff in the old days.
It does seem that 1992 is the date that most sites are going with now. TFwiki also seems to back this up, as does the TFW2005 article.
I do know that some of the release dates used on Jung's (I think that was his name) list for some items have been found to be inaccurate for some things (European Beast Wars), so perhaps this 1992 date for the Constructicons is something that has been verified in recent years.
MIKE
engledogg