My question involves the EDD for the state of: CA

Hello, I received a notice of potential overpayment today from 2014. It turns out they were right and I was wrong.
I was able to find the paystub and I did indeed make an error. I quickly mailed a check for the payment and the 30 percent penalty fee. It was for one week and the amount was $122.20.

My questions are:
Why was the audit so far back?
Does this audit mean that EDD checked all of my UI benefits and only found this one discrepancy, or, did they only audit this particular payroll company?
Is there any way to get ahead of potential overpayments that might’ve been made in the past? (I called and asked if there were others and they said, “No, this is the only one that is posted.” However, my faith in EDD is limited based on how old this error is.)

I keep very good records and was shocked/embarrassed to see this error that I made 4 years ago.

Thanks.