I stopped at Pep Boys today for their $12.99 DIY oil and filter special, five quarts of Quaker State oil and a Pro-Line (Pep Boys brand) oil filter. When I worked there in the late nineties, Pro-Line oil filters were made by Purolator and the same as the regular Purolator line, with only the prefix on the part number being different.
It seems that things have changed. The numbering system is still the same, but when I compared the Pro-Line filter to the regular Purolator, it was physically smaller. To me, this translates to less effective filtration. I compared the filters for my Caravan, Taurus, and Villager and only the Villager filter was the same in both brands.
In a way, I'm not surprised about the change, but this discovery means I'll have to be more careful in the future about buying products based on the way they used to be.