Comparison between variants/configuration of the Chinese Type 64 gas mask

In this video, I have briefly explained the difference between these masks:
1) Type 64A (in original configuration)
2) Type 64A (modified)
3) Type 64B (in original configuration)
4) Type 64B (modified)
Wiki: gasmaskandresp...
Video explaining the exhale valve + voice diaphragm on the Type 64B
Sorry for the below the par presentation since English is not my first language. If you have any questions, concerns, and/or additional information, do comment, please.
It ain't much, but it's honest work.