Supercon 1 was a Minnstf convention held 24–26 January 1992, timed to coincide with the Superbowl in Minneapolis on 26 January.
Elise Matthesen was the guest of honor. (The progress reporty document below doesn't quite say this clearly, but it is confirmed by other documentation in the archives.) (Between 2011 and 2017, we didn't know this, and the history table said "probably not" in the GoH column.)
Supercon 1 had 64 pre-registrations, of which 60 showed up at the con, plus 37 at the door, for a total of 97 warm bodies and a grand total of 101.
While Supercons are still being held (as of at least Supercon 25 in 2018), only Supercons 1 and 2 were Minnstf conventions, with the rest spun off through a mechanism currently unknown to the archivist writing this page.
Supercon 1 and 2 are the only two conventions run by Minn-stf (as far as the archivist knows) that were neither Minicons nor fallcons.
At least, it looks like a progress report, although it doesn't say "progress report". Certainly it was mailed out before the con. Note that while the cover says 1991, the inside says 1992, and it was certainly 1992 because that coincides with the Minneapolis Superbowl and also because otherwise the dates don't line up with a weekend.