The easiest way to tell the difference is to look at the side of the plate in the center. There will be a half circular hole on one side of the plate and not on the other if the tube was made in Holland. If there two holes forming a complete circle, then the tube was made by Matsushita Japan. The Japanese made tubes will also have a dark colored getter. They just aren't Amperex Holland.
Amperex tubes made in Holland have a curious characteristic.
When the filament is first energized, it flashes very bright for a second and then dulls down to the normal soft orange glow. Other tubes do this as well such as Mullard, Matsushita and Ei Yugoslavia. Amperex 12AU7's Currently Available Type Description Price List under construction, email or call for information Mullard tubes made in the U.K are also very well thought of tubes for good reasons. They sound great and last long. The early versions had long narrow ribbed plates.