The DeCoursey ged was one of the first gedcoms added when the site started up. It is mostly correct, but not well sourced. When you come across a profile, it should be edited and sources added. I was asked to leave the DeCoursey note on the profile for now. I have run across a lot of DeCoursey profiles. I believe the originator is no longer living.
Also, my family married into the Mason family in Pennsylvania. I will add what I have to the project. I believe they were English, but I will have to check.