Ab Block

I'm having a hard time finding any $100 invert watermark. I work for a bank so handling a ton load of bills. just today I handle well over of $20k in hundreds and I check for the watermarks to make sure it's a really bill among them I searched all the AB bills & all were from '96 not a single invert. So during my lunch I do a little research & I learned that when this error was discovered 40k notes were return by the banks to the fed. Reserve. I was lead to believe this was a common error & that I shld have no promble finding one.