Where do stem names come from?

I am not setting stems’ names in matrixdef and there aren’t corresponding lines in the choices file, however in customization, some stems have names and others don’t. Why is that? Where in customization does this happen?

It happens here (from customize.py):

    #Create unique ids for each lexical entry; this allows
    #us to do the same merging on the lexicon TDL file as we
    #do on the other TDL files.  NOTE: This needs to be called
    #before customize_lexicon() and customize_inflection()

to fix, add your new POS here (in lexbase.py):

ALL_LEX_TYPES = ('noun', 'verb', 'det', 'aux', 'adj', 'cop', 'comps', 'qdet', 'qpro', 'qadv')