What are the cases where pregnancy occurs even after a vasectomy?

In the 1970s, it was popular for each household to have only one child. When a household had three or more children, medical insurance was only provided for up to two children, and from the third child onward, medical insurance was not available. The government also provided free tubal ligation surgeries. After having two children myself, I also underwent tubal ligation to comply with national policies and to avoid disadvantages related to medical insurance.

But surprisingly, my wife unexpectedly got pregnant even after the surgery. I was so stunned that I had no choice but to undergo an abortion. At that time, the family planning campaign was also active, and abortion was openly encouraged, so I had an easy time getting one. Perhaps because vasectomy was also free, there were many cases of inaccuracies.