I suggest that we cannot know that an impediment existed. You have cautioned me and others that only God knows. But then you say that you know one existed. Perhaps that is not your meaning, but do you see how easily I become confused? The Church teaches that until an investigation has been completed and a finding delivered, that we are to assume a valid marriage exists.
BTW, If I was **forced to guess **

I would probably have to agree with you, that an impediment likely existed. But my language would be different. I would then call this marriage “a presumed marriage”, and would not talk as if it were something that ever existed and was ending. But, as I said, the Church cautions us against presuming a marriage was invalid before the proper authority finds that it is so. So in obedience, I must assume that it is valid. Especially since neither of the spouses has indicated belief to the contrary.
Sincerely,
Dan