There is no CA tax liability for this: "Client expects CA W-2 for 2023 2024 and 2025 also."

That's a Fed W2. With a CA company. Not CA income, unless there is work done in CA. The source is where done and not that the business has a CA address or presence.

"Your client needs to get correct paperwork filed with the payroll dept of his employer to show he is not a CA resident."

Since there was no CA withholding, it seems they already have this info. If they marked all the money as CA for State allocation, that would be wrong. It's not the issuing of the "CA" W2 that matters. It's how it is showing info and how that money was earned. And since NV doesn't have State income tax, there is no other state tax offset. We can't see what this looks like, of course.

"I was thinking if no return was filed for 2023 2024 and 2025 while getting the CA W-2 for those years, California would send a bill."

Typically, for multi-state, there is the break down by state on the W2, and CA would show $0.

Your taxpayer was a resident of CA for some of 2022, and that makes it Part Year resident for tax filing.

There is only Nonresident tax filing if the person worked in CA while not being a resident of CA.