I have a later Corsa extra in SLX and the finish is superb. Bought mine new and some 'decals' are airbrushed to match the paint. My paint, chroming and finish leaves nothing to be desired
In the 90's there was an option for ahead or threaded steerers on the forks but all of the steels were, from memory, 1 inch.
The Corsa and Corsa extra were around for quite a few years so prices vary greatly with paint scheme influencing price as well. I would always try to go for one with original paint.
I'll try and dig some of the differences out and post them up but there is a wealth of knowledge on here so you should have no shortage of advice.
I dont have much experience of the MXL other than a few rides on one that was a bit too big for me but larger diameter columbus tubing on the MXL.
Carlsberg dont build Singlespeeds but if they did.......they would probably look just like mine.
I've spent half my life on bikes.........the other half I wasted