I think THIS is how blackbeard stole Whitebeards Gura Gura no mi abilities. Hear me out, maybe he knew how a devil fruit is born after the user dies and had a fruit on him and it absorbed Whitebeards gura gura no mi powers and he had the cloke so others wouldn't see him eat the fruit to know of how he did it and he ate it, which is how he ackwared Whitebeards powers.
how abput both are true? U know Blackbeard's yami-yami no mi can absorb the powers of living devil-fruit, and he has the "Liberation" techique to puke it all out of his darkness (I have to put it like this cuz i HATE BB so much that i must insult him whenever possible.
So... What if he can absorb the spirit of a devilfruit after the user is dead and release it in another fruit?
I am not sure the Yami-Yami no mi is necesary for this process, but it is an 80% chance it is. (Acording to my gut, of course)