I think one key change is, as noted previously, that before April 2018 the NPPL (with a Class 2, or with a medical self declaration) was good for any aircraft reg, but after April 2018 it is limited to a G-reg (regardless of whether the G-reg is certified or not). After April 2019, or sooner if EASA bring out their intended ruling sooner, an NPPL will be good only for uncertified aircraft...