Two photographs showing the different tails. The first is the standard moulded tail, and the second the flattened and simplified tail used for a period circa late 1960s / early 1970s.
There's a lot of eBay nonsense about 'rare early models' because of the moulded tail, but actually the flattened tailed ones are less common, having had a much shorter production span. But neither are terribly rare, because they're mass-produced pressed glass.
(http://www.holmegaardresource.com/GMB/pig1.jpg)
(http://www.holmegaardresource.com/GMB/pig2.jpg)