We won't know for sure until someone posts pictures of an original heavy sixer having an early serial #(with an "E" suffix), showing the joysticks that came with it. Given that the Atari 2600 evolved toward cheaper, easier to produce parts, my guess is that this style circuit board is an original (early first year) design.
I know for sure as I've already posted pictures of my original 1977 heavy sixer with E serial number. My entire system is original from when it was purchased in October 1977. I know this for sure since it belonged to my grandparents who purchased it new, kept everything in the original box, including the receipt from when it was purchased. People can say my hex discs are second generation or whatever, but if they are original from when the machine was purchased, to me that means first generation.
I didn't realize that you had such an early system. I think your system debunks the idea that there are "1st generation" and "2nd generation" hex discs. It may be that Atari had multiple suppliers of these discs and some are just more rare than others. I doesn't seem to be an accurate indicator of an early production unit. I think the circuit board type/revision would be a better indicator but that is still problematic as parts can be mixed and matched over time. Since you know your sticks to be original, I am curious to know what type of boards are in your controllers?