Page 165 of the 2013 rules says in part:
All unclassified cars will compete in Super Stock (SS) until classified by the SEB, unless covered by a “catch-all” description. To use the catchalls at the end of the specific car classes in Appendix A, start from Super Stock (SS) and work down the classes until a class is found. Such unclassified cars will not be eligible for Solo® National Tours or the Solo® National Championships.
As an example, my unofficial reading of the rules says that a car running in STC under the "Sedans & Coupes NOC (nonsports-car-based; 4-seat minimum;up to 3.1L normally-aspirated)" catch all is not eligible to run at national events.
If you want an official clarification, or to request explicit classing for a car currently covered under the catchall, please do so at http://sebscca.com/.