Amperex 6DJ8 tubes with no shield

I have one pair of Amperex 6DJ8 tubes marked Made in Holland, Orange Globe logo. There is No shield between the plate, grid, cathode structure and the small O getter. I have lots of Amperex 6DJ8s, Holland and USA, but all have a shield. Does anybody know anything about these?
Check out the Tubemonger NOS Picture Library and maybe that can help.

Here is a link to a 1966 6DJ8, which is the oldestĀ  Amperex they have before they went to the A frame: