This is likely the "second" iteration of the design. The first was only in very small numbers just experimental, not any official range, very close to the time the studio opened and often have the coach bolt pontil button.
One thing I have noticed about this range is that in
some of them, the pink can turn rather green when backlit. I do not know anything about the significance of this.
It would relate to the particular batch of coloured enamel used, I imagine, which might be an age indicator, if we only knew when it was used.
The ones that do this tend also to have small, slightly elongated, vertical bubbles. Your's doesn't seem to have too many of those, but it
does have the vertical lines of tiny bits that also go with that.
Try turning it around in different lights and see of you get the green to appear.
