Which other countries do not currently change on the dates specified by the directive?
Well-did not know there was even some EU-ruling on this-always thought it was more like UIC=Trains united. Railways set their international timings in yearly conferences, alternating in big and small.
BUT; Scandinavia is usually out of line. They mostly change before/after their summer holidays and 1st weekend after 1/1. Also the old Russian-memberstates.
The reason to move the change to around 1/1 from the previous late may at that time was twofold:
1.to allow earlier bookings (in the past there was much more of restrictions on that as now-due to insufficient computers etc.) for the main summer periods.
2.to allow TOCs to adapt their timetables to the subsidies, which are mostly on a yearly base-from 1/1 till 31/12.
Still it does not make any sense to me to change it in the middle of works/schoolterms. The 1st weekend after 1/1 would be more fitting. But that was not done, as railways feared to much of work in the Xmas periods.