I did not tamper with my friend's invitation letter. And my friend was actually my girlfriend, so I knew her very well and she did not state any factually incorrect information about her. It may be that she might have provided less information than required. But they didn't contact her. I see her case as completely genuine. Another invitation was from the conference. It seems genuine too.
And about my mentioning of the misrepresentation in future visa applications, I think there are some countries like Japan whose visa form doesn't ask about the previous visa rejections. So, in that case, is there a need to mention it separately?