Basically Joe, every incandescent bulb puts a little dent in the DCS signal. The more bulbs you have, the more degradation of the DCS signal you'll experience. Some cars with electronics are even worse as without the proper choke installed, they will really impact the DCS signal. Atlas cars were somewhat notorious for that issue.
If you don't want to upgrade to LED lighting with proper DCS isolation, then this is a useful tool to identify the cars that will significantly impact the DCS signal. The addition of a 22uh (or higher value) choke to these problem incandescent lit cars will fix the issue as well. My thinking is that if you open the car to put the choke in, why not improve the lighting while you're there! 
