I joined SR in 1979 and was shocked to find that in CH and D VFR traffic would fly in IFR airspace whilst the ZRH controllers didn't bother to use primary.
That night I phoned a mate ex BEA and said that he had to tell someone as we never bothered to look out.
BEA had dirty,scratched screens which we used to protect our trousers from dirty meal trays.
SR issued us with Raybans...foc.
This was still going on in the 90s as I had two airmisses in quick succession, one of which was leaving the holding pattern which was so close I could see the look on the kraut's face and a cigar in his mouth.
WRT Concorde...when it went subsonic it couldn't maintain its previous cruising level and several times both over the Adriatic and Atlantic we had warnings from ATC that she was descending through our airspace.
Adriatic was noise heading over the Alps...Atlantic was technical.
Remember the Zagreb report...if the Trident crew had been looking out they might have avoided the collision.