You'll never find any evidence to say there are only 500. Its a myth that's normally dug up everytime someone tries to sell one. The same rumour has been said about RS1800 Fiestas as well.

Its a fact that Microcat has reg details of a lot more than 500 4x4 Escorts. That totally proves there are more than 500 as they are hardly going to make up reg numbers.

There was a thread about this on RS2000-16v.com years ago.