The Fanuc doesn't care what the file extension is. On your PC it may be TESTPART.NC or TESTPART.COD or anything else. It MUST be a text file, so it could even have a .TXT extension. In the control it's saved as Onnnn (letter O followed by up to 4 digits).
I'm not sure why N015 has V12.0 this is usually an incremental Y command. Should this have been W12.0?
"The sloping line from x40 z160 to x50 z120 doesn't end up sloping just straight." I don't see this move anywhere. What am I missing?