Thank you both
for helping me resolve this question.
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 .