I picked up this calendar today, on account that it was only $3.00.

The calendar is published by DateWorks, an American Greetings Company, in association with Marvel Comics. It retailed for $11.99.

Anyway, while flipping through it, I found this day: May 18th to have an artwork by George Pérez. The artwork reprinted the cover to MARVEL SUPER HEROES ADVENTURE GAME: FANTASTIC FOUR ROSTER BOOK (March 1999).

Here is MAY 18TH, 2004:

For those interested in a higher resolution scan (600x901), you can download it here: MARVEL SUPER HEROES ADVENTURE GAME: FANTASTIC FOUR ROSTER BOOK Cover.