Alright. I saw a better picture. O.k., my idea that the letter is written differently was nonsense. In the meantime, I have seen another picture of a regular sf2ua board and some letters seem to be a bit thicker than others. So, that doesn't say anything.
I still think that this board is not just some regular revision because until now, the letters on six chips have always been changed in every revision. It looks more like this game is the pre-version of the first actual A revision.