CMYK or RGB? for black ink on cardboard

I do layout of the graphics for cardboard shipping cartons that get printed here in the USA and some in Asia.    Company logo, and some safety and environmental marks on the outside of the carton.  We have a library of a couple dozen .cdr files that we use.  I want to standardize as I've found some to be in CMYK or RGB black.

The output files that we present to the vendor are .pdf and .eps.  I am cleaning up our icons in the library to make sure we standardize on one colorspace.  Should I be using RGB 0,0,0  or CMYK, 0,0,0,100  ?

\STeve