A trip down memory lane needed. At pouet.net the Whattaheck party demo is listed as having been released at a NoCrew convention in Gothenburg, taking place from the 4th to 7th of May 1989. That would've been a holiday in Sweden ("Kristi himmelsfärd", "Ascension day"), and is thus plausible.
However - in a textfile I've been adding to since like forever I had marked Whattaheck as having been released at "Rocco's copy party in Gothenburg" - which would've taken place the following weekend (13-14th of May).
I've just spent a few minutes going over the scrolltexts in the demo, and I'm still not a 100% sure. Ghost's screen specifically states "9am on the 13th" as the cutoff date for the copy party demo. The Carebears explain in the Mega Dist scroll that the demo is released on the 27th, "two weeks after the party" after having waited for additional screens (and ours, SYNC's, that never appeared).
Any Swedes in the audience who want to chime in? I strongly strongly doubt a lot of people travelled to Gothenburg two times in one week.
(I'm currently adding a few things to DemoZoo and wanted to get it correct)