I don't know the answer about a bolt hole.
If this is a brand new engine we are talking about lets say just for the sake of conversation that it is true.
What would make you think it is a problem that TT needs to fix ?
This engine has been on the market as is for a long time, it is unlikely any tweaks are going to be made to it at this point.
All reports of the TT91 FS that I have seen have been positive, about smooth running, good power, long life.
It is reported that the TT91 FS is heavier than the other 91 four strokes, but if your plane needs nose weight then this is not a drawback either.