I learned about notch codes the hard way. I had just started working at a commercial lab and I was loading about 50 sheets of E-6 in a roller transport processor, you'd load 2 sheets at a time with the notches facing a certain way.
Halfway thru I thought one felt funny but just kept loading. As soon as I finished someone from the front desk came running back to see if I was done. I found out that the
one that felt funny was a sheet of Plus-X that got mixed in. Plus-X doesn't do to well in E-6 chemistry. Half the sheets of E-6 where ruined and I spent the rest of the day
dumping the chemistry and replacing it. I memorized all the notches after that.