Been to NJ and NY a bunch.
Has there been a case where CA has came an confiscated someone's legally killed cat mount?
You can't even bring the mounts into the state. They are listed as a "prohibited" item. The only exception for trophies is for cats killed prior to 1990. Note the following:
https://www.wildlife.ca.gov/Conservation/Mammals/Mountain-LionThe passage of the California Wildlife Protection Act of 1990 (Proposition 117) by California voters established that mountain lions are a specially protected mammal in California, and that it is unlawful to possess, transport, import or sell any mountain lion or part or product thereof (including taxidermy mounts). An exception to this law exists for possessing or selling taxidermied mountain lions or mountain lion parts:
No person may sell or possess any mountain lion, part or product thereof, unless he is in possession of a valid, nontransferable permit issued by the department. A permit shall be issued by the department only to:
any person who can demonstrate that the mountain lion, part or product thereof, was in his possession on or before June 6, 1990; or
a nonprofit museum or government-owned facility generally open to the public, or an educational institution, for display, exhibition, or storage, for a bona fide scientific or educational purpose as determined by the department. Permits shall be made available to department employees for inspection upon request and may be revoked by the department for failure to comply with the terms of the permit, this section, or Section 4800 of the Fish and Game Code. Any person issued a permit or a tag from the department for a mountain lion, or part or product thereof, prior to January 1, 2014, shall not be required to obtain a new permit, provided he maintains and makes available his existing permit or tag upon request of a department employee.
Even if the cat is legally killed someone in CA can't bring so much as a whisker into the state legally.