The original QC'ed netCDF data set does not include "Time" as a variable.  Newer versions of NCPLOT required a time variable for plotting of any data.  The netCDF file with _Time added to the name was generated from the original QC'ed data set, with the variable "Time" added.  There are no values for the Time variable (filled with '_'), and all other data in this file are identical to the final QC data set.