Well sorry to say this but even under your grandfathers time ivory trading was awful. I say this as a Kenyan.
The leadership of the Government of Kenya at the time were involved in this and it led to not only to a culture of large scale corruption but also to uncontrolled killing of elephants.
The good side that was looked at at the time: Elephants no longer invade human settlement and profit can be made from it. The downside no one cared about was the long term survival of elephants.
Unfortunately the corruption element is where everything broke down, it wasn't that the industry was pushed underground - it was that the elephant is not an animal that can be farmed or domesticated & further - the demand outweighing supply only meant that regulation couldn't be enforced anyway. Your grandfather played a role in this which is nothing to be proud of.
Today it is the same thing you cannot regulate elephants and farm them because they cannot be domesticated and have lifespans as long as us.
I can say this having elephant ivory in my house from my elderly family members too - also not a good thing. They did not trade it but they bought it being unaware of the consequences where unrestrained human and economic growth eats into the limited factet of nature's abundance.
Good thing though: Elephants now adapt evolutionarily and grow old without tusks.