Zeros can shift slightly for various reasons. When I help shooters with the Gen2 PSTs, I highly recommend that once you bottom out the turrets in step 1 that you come back up about 1 MIL or 2-3 MOA before removing the outer turret. Once removed, continue with disengaging the inner turret and proceeding with getting your zero and then putting everything back together as they instruct. Once finished and you and you have reinstalled the outer turret with the 0 lined up on the index line, you should have a MIL or 2-3 MOA of down-travel below your zero. This little bit of wiggle room can come in handy should you need to adjust your zero down a small amount; then you can just loosen the 3 outer turret screws and "slip" the outer turret back to the zero line, re-tight the 3 outer screws and you'll be GTG again without having to get back to adjust the inner turret