I also thought Wuff that it could be a commissioned peice but is obviously not. There is a similar one in the catalogue but without the 'streamers' and has the Royal Arms in the centre of the facetted face on the 'issues of 2001' page.
May I ask why it is "obviously" not a commissioned weight? The fact that a similar "production run" weight might exist, is not sufficient for that statement: there are several examples of such weights with only small modifications.
BTW - which weight are you referring to? This one
? This would be completely different - not only no streamers, but also no controlled bubbles and a different "background".
In the description it is said that there is a small bubble inclusion under the engraving of the Queens head, could this I wonder be the reason for the Queens head?, to cover the bubble?
If the "bubble" actually is a bubble (there is a tiny mark visible on a picture of the front facet, nothing visible on side and back views) and unwanted, I would be fairly sure the weight would just be destroyed (if not sold as second with the original design) - not that bubble "hidden" by a fairly complicated design. In the latter case this sample wouldn't have the streamers and controlled bubbles and different background - so this explanation is definitely ruled out.
As I had stated, a trial piece cannot be excluded for sure - but if you want me to place a bet, I'll bet on a commissioned weight