Dave,
Yes, NCPlot is looking for the program ID in Fanuc format. The O word must be the first character on the line:
%
O1234(PROGRAM1)
G1X...
...
..
M2
O2345(PROGRAM2)
G1X..
...
..
M2
%
Is the N word always the same when it appears in front of the O word? If so, you could do a search/replace to remove it before using the Save as Separate tool.
Regards,
Scott