As far as I know all Sierra's, including the Cosworth, got the smoked rear lights and clear front indicators with the 1990 facelift. That was also the same time the Cosworth was changed from 2wd to 4x4. So I think any 2wd with clear indicators and smoked rear lights had them changed afterwards.

BTW, why is it difficult to find a 2wd bonnet? The 2wd cosworth bonnet is the same as any other sapph bonnet, right? Strangely in the rest of Europe all facelifted Sierra's from 1990 had the short bonnet and all Sierra's before 1990 had the long bonnet, while in the UK sapphs had the short bonnet and hatches the long bonnet, not depending on the 1990 facelift. Or is the short bonnet from a standard Sierra different from the 2wd Cosworth bonnet?