Hi Mate
I'ts whats called a buddy bottle. I would think the 300 bar is the test pressure not the safe working pressure (fill pressure). The 200 bar seems more likely to be the safe working pressure. You could use it to decant from a bigger bottle, and fill it to the safe working pressure from a larger bottle.
If the bottle is not within the test date, I would definately get the buddy bottle tested before you fill it to 200 bar.
Regards
Steve