This is what I have been advised, however Im not sure if its right enough or not, so please correct as appropriate:

In 1986, the first series 2 Escort RS turbo was made and registered on a D. The car at this point was manufactured in Germany until 1987 therefore as was some early E registered. The german metal gave a strong shell and cars of this period of time ere found to have shown little signs of deteriation. In late 1987 they began manufacturing the Escort Rs Turbo in Spain until late 1990. The spanish metal wasnt as strong and has been found to be more prone to fatigue. By 1991 they realised this, and went back to using the german metal for the final year of manufacture in 1991.

So basically saying the D & H regers have better shells? Enlighten me...