I received a notice about not paying a ticket, 6+ years after I had paid for it. Lucky for me, I still had the paper receipt and so I went into the SF courthouse to show proof of payment. After reviewing it, the clerk told me that it looked like their IT modernization had erroneously marked my case as being unpaid. I can't imagine how very painful the resolution process would have been if I had not kept that receipt.

This is why I laugh at the “convenience” of a paperless world. Still might not help but at least a paper receipt is something.

Yep. That is most likely what happened. Really put a dent in plans but thankfully I can uber!