This could be one of two scenarios:
-The chapter could be recolonizing/reorganizing and the natl website just hasn't been updated; or
-The women are keeping the chapter going underground without official sanction. (Although flyers aren't very "underground," LOL.)
To be safe - email the sorority's national office and ask what the status of the chapter at your university is.
Bravo to you for being smart and checking this out!!