The while thing about Lisa being on the fact of life of that is that unless you are in your 30's or older you prob didn't see the show and its not one of those shows that shown in reruns over and over like mash or the cosbys
Plus after facts she got married and left acting behind
So the only ones who had a chance of knowing who she was did but chose not to out her
First, it's still in reruns and always has been afaik.
Second though, there are a lot of players old enough to have known who didn't - Denise, for one, Artis, that other returning jerk, Jeff, etc.