I presume your asking a question? If so, then certain 2012 models had some issues relating to The panel. I suggest you google the question for a more complete answer regarding the difference, it will tell you everything you need to know.
Current model rMBPs are just as reliable in terms of working out of the box, the 2012 rMBPs had no inherent problems aside from some lagginess being reported and LG screens exhibiting image retention.
If you get an LG screen you may still incur the IR, and for some people they still get the lagginess (though I've not really noticed it on my rMBP)
There is no difference in terms of build quality between the two years.