I've wondered if DL didn't stand for deluxe, F for featherweight, and E for economy. I've never found any solid evidence of this, but it works for me.
Perhaps EG stood for extra good?
David Royal has recently completed a great book about the Savage 99. I highly recommend it for anyone who has even a passing interest in them. Doug Murray also produced a handy little pocket guide of a book about them.
Arthur Savage was a very interesting man.