Background checks are unregulated.
Is a previous employer allowed to tell a prospective employer you were fired when you were not in Nevada?
You dates of employment and what position you held.
Yes. The legal implications would only be if they lied and caused you harm.
If a prospective employer calls your previous employer, the previous employer can say whatever they feel is true. If you don't want a bad reference, you may not want to put your previous employer on the application.
A past employer may give a prospective employer an overview of the employee's employment record. They can give their opinion about the employee's character.
A prospective employer may be interested in your health because many employers pay a portion of their employees' health insurance. Health insurance premiums may be higher if you are in poor health or a regular smoker. However, a potential employer is not legally allowed to ask questions about health during an interview.
I don't know about in California but I heard that an employer is not allowed to tell anything about an ex employee unless used as a reference. If you just use the employer as a previous job all they are supposed to be allowed to verify is that you did work there and the dates. However if you put them down as a reference and a prospective employer calls them they can elaborate on your character as well.
Yes. Legally, they are allowed to say anything that is factual and accurate.
All employers can ask that with zero liability.
prevent discrimination
This shows that your employer allowed you to leave on good terms. It is like a recommendation letter and allows future employers to feel more confident in hiring you.
It remains legal in every state to tell the factual truth about employees and former employees. "I fired Jim for attendance problems", can never be the basis for a defamation suit IF ... 1. I DID fire Jim, and 2. My reason was his absence record. Jim need not agree with my decision to make my statement factually correct.