You are absolutely right this can happen, and a badly designed product could deteriorate faster than expected. But this is not what happened here. They had to know very early, since the heatsink cannot be assembled.

AMD say that only a small number of cards are affected, but if it is true, this is even worse: why not scrap these cards? It doesn't make sense at all.

We all know that all manufacturers at one stage or an other will face this. What is wrong and surprising is how AMD chose to handle it: surprisingly poorly.