French Cover With A Unusual Shape Of The Cancel.

One of the cancels on the back of this old cover from France has a bit strange form. The shape of the cancel at the middle doesn't correspond with one applied on it. It looks like a additional piece of paper was glued on it.

Railway cancel ("ambulant") : Le Havre à Paris

Agreed, it looks like a paper patch was applied over the middle cancel. I wonder if the original cancel had the wrong date and the clerk glued on a patch with the correct date? Or maybe it was a repair done after the fact, to seal a hole in the cover at the intersection of what looks like 2 mismatched folds. What does the inside of the cover look like at that point?

Edit: How does the folded-letter open? Is that paper patch sealing the letter closed, like a poor-man's sealing wax seal, and the cancel doesn't line up because someone unsealed the letter at that point and simply it doesn't line up after being opened?

Thank you both
for helping me resolve this question.

ZebraMan,
You have gave a very good and detailed explanation .
This is precisely what I meant. Yes ,It looks like the small piece of paper was first cut off a noter envelope and then sticked on the original cancel probably to repair it as you've suggested . I must say I haven't tough that the date could be the wrong one.
I have only observed that it doesn't line up correctly and it's different from the other cancels. I have checked it and it seemes that there is no hole in it. I could only guess wath is the reason for seeing this,but I tink that the scissored pice of paper was glued there deliberately .