the "90 spec" was the 1990 facelift onwards, which gave the smoked lights at the rear, clear front indicators, deleted the under dash speakers and gave a larger glove box on the passenger side plus the addition of the drivers side glove box, the different central locking setup (which meant different doors), different heater controls, the introduction of all disc brakes on the dohc engined cars, different seat fabrics, true twin din centre console stereo set up, a redesigned upper and lower dash board (all 3 parts), remote boot and filler cap opening, deletion of the boot push lock and a different shape for some of the wiring plugs and sockets

the "92 spec" facelift saw the wrap around upper dash, different heater controls yet again, a smaller instrument cluster, different door cards with 4 screw door handles instead of 3, electric sunroof options, no more trip computer, single rear number plate light (other than the cosworth, which retained the older double light set up), body coloured bumpers across the range, abs as standard on the gls models (previously only standard on the ghia and cossie models, there is some debate as to when they standardised it on the xr range as some still came without and some were badged as ghia models on the estate versions, they were optional on all but the cossie on everything before the 90 spec, even the 2000e) and so on and so forth, and they changed the plug connector shapes again, now including a triangle and square shape to replace the older round and oval versions

i'm sure there were other changes but these are the main ones that are noticeable and can tell you if you've had a car made in one year or another and also the easiest things to change if you want to update your car to the latest specs

everything is interchangable along the way