James Mattis and myself are probably the two best students of Calif. law on the forums. Other guys have made specific studies of other states; you can tell whether or not they "know their stuff" on whether they know what specific code sections are relevent.
Let's have other people chime in if they've studied other states.
Another thing: "carry law" and "use of deadly force law" are two ENTIRELY different subjects. California's standard is "you can use deadly force when in fear of life or great bodily injury". There's no specific retreat clause but there's also no "support for good Samaritanism" which is why I believe in "verbally" objecting to BS and then defending if the baddies turn on me.
"Use of deadly force" law is generally clearer and more sane than carry law, and varies less between states. Any criminal defense lawyer should have a solid feel for deadly force law in your state, but carry law can be so byzantine, so illogical and so complex cops, DAs and even defense lawyers may not have a clue, especially in heavy defense prohibition states like California.
NOTE: I'm NOT a lawyer, YOUR MILAGE MAY VARY, yadayada. But I'll say this much: don't ask a cop, that's the least reliable source possible.
Jim March