Identify production code on german/chech gas mask.

[Alexz666]

Ok, so I have this gas mask, its a checkoslovakian Fatra FM1d mask but with filter from german civil gasmask VM40. I have seen a few of these and I know the mask is not switched since I've seen others.
I find lists with the other production codes like RL1-38/4 and so on for the german made civil masks VM40.
This box is marked RL1-42/9.

Can anyone help me identify more on this code.?

I suspect its from Sudet when it was annected, am I right?

Thanks!

[timothy]

Could very well be a foreign mask taken into service by LS I have seen foreign ones before similar to this one. LS used a lot of foreign helmets so why not gas masks. I kinda of like it. filter is definelty LS Volksmaske model. timothy