You'll need to recreate the original then amend it.     Probably be difficult without recreating the original federal as well....how much $$ in taxes are we talking about?  Will it be worth what you'll charge him to do all this recreating and amending for what its worth in tax savings?

Did he work in CA but live in WA? Different answer, if true.

Otherwise, did the TP sign the returns, attesting that all information included therein was true, correct and complete?

Apparently, all information was not true, correct and complete.

Very true, I only addressed the logistics of amending the state return.

That's the big question is whether it is worth it.

I think that they had capital gains in the $1000s from the sale of property and some rental property income as well.

I think the play here is to find someone in CA who can answer the question about the different tax rates for the different residencies.

I chatted with FTB and wasn't sure.  Not the brightest bulb.

Thanks for help, C

California does the 'tax computation' on ALL the income (as adjusted for an CA tax law differences).

That tax amount is then multiplied by the ratio of CA source income divided by the total income.

Depending on the other state and the reciprocity agreement between the two states, there should be an OSTC in play based on the double-taxed income.

Also, capital gains don't get any special treatment by CA; all taxed at the going ordinary income tax bracket.

Washington has no state income tax. Not sure when their capital gains tax when into effect.

If capital gains and rental property are all in CA, the tax as a resident vs nonresident may be the same.

hmmm - I didn't see anywhere that the OP mentioned Washington ?  Only one responder; time to get my eyes checked 😉

Its in the title of the question

@Just-Lisa-Now-  Yes, but maybe he meant D.C. 

ah.... so it's official.  Eyes be bad, that and missing the obvious as I read the question only.

No OSTC then.