This is a wrong assumption. The working pressure for our 3 liter tank is 232 bar, though you will notice that the test pressure is 450 bar. This means that this type of tank is suitable for a maximal working pressure of 300 bar.
Our setup is a tank with a working pressure of 232 bar and 232 bar valves.
Of course it would be possible to get the same tank with a working pressure of 300 bar, but in this case you would also need 300 bar valves. This is not a huge problem on the diluent, but there are no 300 bar M26x2 valves available that can be used for the CE edition.