The Sovtek Green Big Muffs listed here have been lumped into one category. I now realize there are physical as well as electronic differences in the green versions. That being said my experience watching these over the last five years is that really does not have an effect on purchase price. These green muffs are popular and all models sell well. Average sale price has been the same for almost two years. If someone posts a specific date of manufacture I will add that category.