States are not great at preparing 1099s. 

You might start with the AZ forms instructions and commentary:

https://azdor.gov/individual-income-tax-filing-assistance/identifying-other-taxable-income
https://azdor.gov/forms/individual/form-140-arizona-resident-personal-income-tax-booklet

Serveral states do not tax retirement income. I do not know if Arizonia is one of them.

Pensions are generally taxable in the state of residency. 

Don't forget that Firefighters are Public Safety Officers https://www.irs.gov/pub/irs-dft/p575--dft.pdf page 6

I must respectively disagree with you. Many states do not tax retirement income whether that retirement income comes from the state you live in or someplace else.

But the exemption from tax is usually accomplished by a subtraction from income on the state return.

Most states start with federal income and adjust it up or down.

You'll probably have to determine that for yourself.  Since retirement income follows residency, you'll need to apply the law for the client's state of residency.  And you'll have to determine if it qualifies as a disability retirement by asking your client some questions about their circumstances.

While there are several states that don't tax retirement income, there are many that do, and in different ways.  I wouldn't rely on the 1099-R issuer to know the answer.