I am not familiar with the form FD4100A and cannot seem to find it on the CA-DOJ firearms web site...
http://ag.ca.gov/firearms/forms/
There is a form FD 4010A which is used for new resident moving into CA after 1998 to register all guns you are brining into the State.
http://ag.ca.gov/firearms/forms/pdf/...629510b375a951
Also, when I sell off a piece (to enhance my C&R collection), CA wants you to report that you no longer own the piece as well. That is this form FD-4036. Filing this form is free.
This form is important as if one of your guns is used in a crime, they will not come knocking on your door as you have reported it, previously, as no longer being in your C&R collection and in your possession.
http://ag.ca.gov/firearms/forms/pdf/nlip.pdf