I'm not really sure where to file E-X cards. Trading Card Database lists them as both Fleer and Skybox ranges, which was the same company at the time. I think they just flipped a coin to see which company name got stuck on the cards in a given year.
Card Number 807: Skybox E-X2001, 1998; #13
Card Number 808: Skybox E-X Century, 1999; #4
1999, the year when everyone referenced the end of the century...