I have never read both these stories anywhere in Vyaas' Mahaabhaarat, but it is a popular story outside of Mahaabhaarat

After the Mahaabhaarat war, King Dhritraashtra asked Krishn - "Hey Krishn, I don't understand the reasons for my losing all my 100 young sons in this war when I have apparently done no crime." Krishn out of His grace granted him Divine vision to look back in his previous births.

Dhritraashtra discovered that 50 births back, he was a hunter and once threw a burning net on a tree causing a 100 birds to be burnt to death while remaining flew away but they also became blind due to the scorching heat. Due to the effect of this sin he was destined to remain blind in this life and also lose his 100 sons.

Dhritraashtra then enquired - "Krishn why didn't I get punishment then and there and in that birth itself, or in other future births, for the that great sin I had committed? Why now?" Krishn smiled and replied - "Your past sinful deed had to wait for the appropriate time, up to 50 births during which time you could earn and accumulate enough pious deeds to merit you to be eligible enough to get 100 sons in one life time so that your previous sinful Sanchit Karm could instantaneously confront you with the effects of that evil action."

This then is the Law of nature and effect of Sanchit Karm.

Another Version of This Story.

After the Mahaabhaarat war, King Dhritraashtra asked Krishn - "Hey Krishn, I don't understand the reasons why I was born blind in his life. I can see my 100 previous births and I don't find any such sin committed that I should be born blind in this birth. " Krishn out of His grace granted him Divine vision to look back in his previous births than 100 births.

Dhritraashtra then could see that in his 105th birth he committed some sin because of which he had to be born blind in this birth. Thus this was the result of his previous sinful Sanchit Karm. That is why that was the Law of nature and effect of Sanchit Karm.