There is a little bit of info here about the Nipper dog trademark re-introduction.
http://www.cedmagic.com/home/cedfaq.html#oneeleven
It seems like for some reason RCA chose to discontinue Nipper a few years after his re-introduction because the Nipper trademark is owned by other companies in other countries (such as EMI or JVC) and RCA could not market products bearing the Nipper trademark abroad. This may not be exactly right but I know it had to do with the difference in the trademark's ownership in other countries.