The German edition of Tom's Hardware delivers news that NVIDIA is no longer shipping higher-binned versions of its Turning GPUs. The company pushed these ships for factory-overclocked video cards, with the A-dies promising better overclockability and likely a better power consumption profile. This is now coming to an end, there will be just a single version.
TPU speculates NVIDIA introduced the A-dies due to yield issues:
This move by NVIDIA - on which we reported firsthand here at TPU - was likely a solution to somewhat less than ideal yields for its TU-104 chips, ensuring partners could provide the best experience to users who were willing to pay the most. The fact of the matter is that AIB partners were locked out of overclocking non-A dies should they acquire them (which were going for less than their higher-binned A-cousins), though the end-user would not see such a limitation - besides the one imposed by the expectedly less capable dies present on those non factory-OC'd cards.