Just to add a bit more confusion, these are the "offical" designations......
as found in the Ford brochures and press releases.

* The info is from Jeremy Walton book "The Cosworth Fords":

Sierra 3DR: T03

RS500: T31 / T04

Saph RWD: T03

Saph 4WD: T03B

Escort Cos (big turbo): T3 / T04B

Escort Cos (small turbo): T25

* Prior to publishing, this book was checked for accuracy by Ford personal.