Only time I've ever seen the left side screw and a rotary extractor is on a reworked gun where the Roller was upgraded to a rotary extractor. No rotary extractor original guns had the screw as the rotary extractor has nothing to do with that area of the receiver to retain it. The breech blocks are simply machined for the rotary extractor to fit into the side of the block, and they operate off the block, not the receiver. So if your friend's has a screw in the left side it's an early action that someone put a later breech block and rotary extractor into.
I'll happily takedown all my rotary and sliding extractor Rollers if it helps to show how they work here.
I'd suggest your friend has such a gun, and he could remove that screw and store it away and the gun will work perfectly without it in place.
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