It is such a pity that these threads keep popping up over and over (1) because some owners never bothered to follow up on the issue despite knowing their bike could possibly be affected.
I think that the reality is that the majority of owners of first-generation TEXs never knew about the issue and are not members of this forum. I think that it is really the Do It Yourself oriented owner (like me) who is likely to join an owner's forum looking for pre-purchase information and (more critically) post-purchase maintenance and repair information.
Also, owners that did notice their engines getting noisier, were (and are) frequently told by their dealerships that "they all sound like that". The real fault is that many (most?) dealerships never knew (or never acknowledged that they knew) about the problem or the solutions.
I knew about the head recall before I bought my '13 TEX and it was the first thing that I asked about when I went to see the bike at the dealership after seeing an advertisement for it. I was fortunate that the dealer (now closed) had proactively done the head replacement at 500 miles before I bought it.
As an interesting side note, the dealer told me that they had sold four TEX's that year and three of them (including mine) were actually transported to another dealership to have the head replacement done (after my dealer ceased being an authorized Triumph dealership). I am not sure if all three were done proactively (without symptoms). I did confirm that the work was done on mine by contacting Triumph North American corporate directly.