Since I am a member of my sorority who chartered a chapter and our founding mothers are still alive... I will put in my thoughts on the subject... chapter chartering sisters are referred to as chapter founders or founding sisters. Our organization founders are referred to as Founders, Founding Mothers or Black Diamonds. I never really paid any attention to what other orgs say but I know that my orgs Black Diamonds refer to us (chapter chartering members) as chapter founders. So I guess, for us, its OOOKAY! I say all that because I think it will definitely be interesting to see, years from now, if sorors have a problem with chapter chartering sisters being called founders....
And I do agree that sometimes those who did much of the leg work toward starting a chapter end of graduating before the chapter is chartered, and likewise newbies come in and do little more than sign their name. So I like the term founders for those who did the real work (or were hanging around while it was being done.
FYI: I do, at times, refer to myself as a charter member when I speak to other greek members who use the term.