I need to see the original document myself to work out what my father is on about. He explained it as being a document that pertained to me - but I might have misunderstood. Whatever he is looking at, he clearly seems to think there was a possibility of another child. That being said - he's not very analytical, so it wouldn't have occurred to him to investigate further (nor would he have pressed the matter with my mother). If he asked and she said no, that would have been the end of it. I, on the other hand, want to know either way.
I'm particularly curious because I have failed to have a DNA match with his cousin, so one of us is clearly not related in a fashion in which we think - so that coupled with this information has made me consider the possibility that he might not be my biological father either. It's all a bit of a mystery.