If this had happened in the LTMA the approach controller would have had a flashing alert on the radar that the wrong QNH was set as soon as they were descending through the TL, surprised there’s not similar for CDG.
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On the subject of do pilots check others transmissions for their own SA: yes they do. Multiple airports in our sector, we prefix the relevant airport when issuing QNH to save the next couple of transmissions being “confirm QNH?” from a pilot inbound to a different airport with a different QNH.