John,
In the last ADS meeting, Dan (or perhaps it was Gordon) that they use 9500 series errors in when they haven’t decided how to assign that error code yet. So you have to contact Dan or Gordon for those. They normally wouldn't be documented with a final error code yet.
Thank you Susan. My error (in stable BR! 4.2) turned out to be a grid/list syntax error. I documented it on the wiki as best I could. I'm sure when they do the final error project that they'll get the documentation wiki updated with better answers.