California certainly doesn't try to be too informative for part-year filing requirements.  Technically, I think a part-year resident has to file, if their total annual income exceeds certain amounts, even if none of it came during the period of California residency. Because, how does Sacramento know that until you tell them?  And if 5% of your client's income came in the last three weeks of December, and the California tax would be $500 if they had been full-year residents, then they owe $25.

But I would not throw these clients to the wolves, by telling them to find a California preparer to do their Arizona return.  First, the fees would probably be twice as much as yours because, you know, it's California.  Second, have you followed what kind of mess the Arizona return is going to be this year?  The legislature had better things to do than address the issues of conformity to the new federal law, but many of those adjustments will be enacted in January or February.  Which ones?  Well, the governor has her list, and the legislature has its list.  The governor controls the Department of Revenue, so the forms will show her preferences, with the instructions pointing out that they are not yet enacted, and probably not mentioning that others may come along also.  Your client deserves someone who is following this situation already. 

And I agree with the comment, that California is likely to track down anyone who files with a California address even if they never set foot in the state.  Like my elderly client, whose daughter in the Bay area was using her own address for filing Mom's 1040, so IRS notices would not go astray.