Sorry Jimmie, I had assumed that by 'shroud' you meant the whole tube that is used to cover the otherwise exposed spring.
So, I have now given my pistol a good going over, and have now come to the conclusion that the plastic cover could very well be non-original. Although the cover is exactly the correct size and its ends are well finished, there are clear indications that the gun has been taken apart and I can detect vise jaw marks. So unless another example turns up, I think we should assume that there never was a plastic shroud variant.