Another e-mail from SuperChips sent 2 minutes later:

"Sorry for the confusion. We have chips for the 420 Mercedes but not that year. The dealer you called looked at the listing and did not confirm the year. The computer is different between years and there are some we do and some we don’t. Bottom line is that we have chips for some earlier 420’s but not your year.
Ken @ Extension 3030
Thanks for your interest in Superchips."