I doubt that CDFG would regulate Boulengerella, Ctenolucius, or Xenentodon. True gar are native to the eastern U.S., grow to large sizes, and, in CDFG's eye, if released could survive and potentially threaten the salmonid populations. I doubt they would view Boulengerella, Ctenolucius, or Xenentodon in the same light.
Many LFS owners and employees simply lack the information or wherewithal to wade through the California Fish and Game Code and Fish and Game Commission Regulations to determine what is legal or illegal. This is made even more complicated because the statutory list in the Fish and Game Code and the regulatory list in the Fish and Game Commission regulations DON'T match! The statutes give the Commission the authority to promulgate regulations and list additional species as they see fit. Thus, someone referring only to the statutes, for example, would not know that snakeheads are prohibited in CA because they are only listed on the regulations. Nor does the CDFG have an easily accessible list on their website. You actually have to comb through the California Code of Regulations.
LFS owners know or should know the obvious ones like piranha, FW stingrays (Potamotrygonidae), snakeheads, and gars, but the presence of "fake" and "real" gars makes things more complicated. Moreover, wholesalers don't always know which species are prohibited in each of the states to which they ship. I'm not defending the actions of wholesalers and LFS owners, merely explaining how prohibited species could "accidentally" end up in a LFS in CA.