I meant to go on but submitted by mistake! Anyway...
Display technology was still basically small modules with dials. Externally they looked all the same, but the modern stuff the needles were being moved by servo-motors controlled by this newfangled 3rd generation computer tech'. I was involved at the time with a new plane called the A320, and this meant glass cockpits and fly-by-wire was only just making a major break into the commercial market.
So for Concorde although the computing part of the avionics was massively upgraded at some point, it is likely that most of the dials and switches did not need to change. It would be difficult to perceive much difference just by looking, as most changes were behind the scenes.