I don't remember it as ever working correctly. The cabin column often shows E when the fare is for premium economy. This applies to BA (PE is WET) and CX (PE is WRE) at least. Expertflyer is an american company and they hardly know what PE is in the USA.
I had to make my own XLS with the PE fare codes for various airlines.
ITA matrix also has trouble with PE fares and won't find them with a short haul connection (since the short haul connections don't have PE). Another issue that would not occur if PE was more common in the USA.