Urgent - PVC Shower Pan Pierced By Screws - Will This Cause A Leak?

I am having my shower torn out and completely rebuilt.
The trademan who is doing this (and who has done exceptional work for me in the past) has installed a PVC liner 7 inches up the sides of the shower and over the curb.
However, when he installed backer board over the PVC liner, he installed screws into the backer board that were about 1.75 to 2.00 inches above the bottom of the liner where it rests against a sloped subfloor, piercing the PVC liner at that level behind the backer board.
He intends to lay down a layer of mortar on top of the PVC liner to create a sloped surface to lay the floor tile on. Thus, the height of the screw holes (and the punctures in the PVC membrane) will be even closer to the finished shower floor by the time the tile is installed.
This trademan says that he installed a bead of caulk to prevent the PVC liner from leaking where the screws penetrated the liner, but I am still extremely concerned that integrity of the PVC shower pan has been compromised by the screws that pierce it.
It is my understanding that the PVC membrane should NOT have been punctured at a point so low to the bottom of the pan.
I would also like to know what would happen if the PVC membrane on top of the curb is pierced by screws when backer board is installed on top of the curb. Will this create create a potential for leaks as well?
If screws should not pierce the PVC vinyl membran, what is the appropriate way to fasten backerboard when a PVC liner has been installed?
Am I justified in being concerned about the potential for leaks?
Please respond ASAP as the trademan has not installed the tile yet, but plans on doing so very shortly.
Thank you.
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With the caulk and backer board, it is well sealed. Thee will be tile over that too right? I don't see any reason for concern. Done right, water should never get there anyway.
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The screws piercing the PVC membrane are 1-3/4 to 2" above the PVC membrane lying on the subfloor, but on top of the PVC liner a sloping mortar bed will be added as one cannot place tile directly over the PVC liner.
This means that after the tile on the shower floor is installed, the screw holes will be much closer to the bottom of the shower floor than the 1-3/4" to 2" that I listed in my original email.
Sorry for posting my inquiry so often. I had posted it and deleted it several times - each time revising it a little.
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