I think Neillite was very similar Bakelite, but maybe a bit different formula. J.R. Neill, inventor or Neillite, joined Watertown Manufacturing Company in Watertown, Conn. In the Watertown Book of Plastics from the early 1940s they make a distinction between the two. Also, the cases feel different. The Bakelite cases feel more substantial and heavier than the Neillite.
This image is one of the earliest ads for KEM cards that I have found, and it references the Neillite cases.
In an interesting aside, in the Watertown company bowling league at the time, all the teams were named for different types of plastic. ** Found the bowling league info. It is from 1951 **