I have pondered this for some years (off and on, I really do have other things to do) :-)
And have come to the following conclusion: The rear (stock end) most catch is for general manual cocking so the bolt doesn't have to be pulled all the way back, and the front most catch is for the first chance to stop multiple discharge after the trigger is released, the then the rear catch acts as a safety catch for either bounces off the buffer the for underpowered ammo.
Does anyone have the real story?
BTW: You guys that hate NAC guns so much remind me of a family reunion at the DuPonts when all of a sudden some mixed race orphan shows up and claims she is heir to the fortune.

Doug