So I have noticed this for a while, but wanted to find some more of The Black Series 6" 43: Darth Vader figures with newer date stamps before jumping to any conclusions. The Vader figures with older date stamps seem to have more of a classic Helmet Dome, while the Vader figures with newer date stamps have what appears to be a larger wider sized Helmet Dome.
• Smaller Dome - Date Stamps 71531 - 71671
• Larger Dome - Date Stamps 71671 - 71871
I have found dozens of each version at retail, so they are both out there in large numbers. Not really sure if these are just production errors or a actual change though.