Too bad. I don't have such clear-cut proof. Only that I appear in a statistics from early August 1992 with my ancient address under the mouse COE in Usenet. I must have been online for at least 12 years by that month, assuming the statistics included at least July. My first archived posting is a bit later and then already from the Maus ST2 (of which I was one of two operators) from October 1992. I feel old...
At Die wunderbare Welt von Isotopp I found the original article.