The good news is, the old "non-P" paper is about gone, as I've learned through this thread from REAL painters (as opposed to myself). When you order 400, you get P400. If you never knew the difference, you were happy until you read this post!
This is happening everywhere in our lives. I went to Walmart yesterday (which used to be Wal-Mart before Sam Walton died). All I wanted was regular Alka-Seltzer that I used to buy in the 1960s. The clerk directed me to what she thought was the stuff. I found Alka-Seltzer Gold, Alka-Seltzer Plus for Cold and Cough, Alka-Seltzer Plus for Cold only, Alka-Seltzer Plus for Severe Cold and Flu, Alka-Seltzer Power Max Gels, etc., and Walmart brand fizzies that are half the price but worked just the same. NO ALKA-SELTZER ORIGINAL. I found out 10 minutes later, Alka-Seltzer Original is in a different aisle. I rest my case.