Normally Intel releases information about the improvements and upgrades for products when they have being preformed and applied already, before that any information will be kept for internal usage.
The reason why the Intel® Centrino® Advanced-N 6230 adapter has a different special feature, Passpoint™, from the Intel® Centrino® Advanced-N 6235 adapter is based on a decision that Intel has taken, but you can continue to check from time to time to see if there is any change on this product.
But, with respect to the wifi component of the physical card, does the 6235 have a "different specific feature" from the 6230 (a distinction which might reflect nothing more than a marketing abstraction from real, on-card hardware specifications), or does the 6235 have a different hardware specification which limits its ability to be certified as Hotspot 2.0/Passpoint compliant?
I'm not looking to raid the hoard of corporate secrets or anything; I would just like to know if the difference between the cards in this one area is ideological (e.g. Intel's choosing to ignore Passpoint certification) or material (i.e., the 6235's having wifi innards different [enough] from the 6230 to remove it from contention for Passpoint certification). An answer in either direction would help me make the choice of which card to keep in my laptop going forward.