I think Im reopening an old pandora box with this but oh well...
I wonder how Devil Fruits work. Supposedly only 1 of each exists at a time... so... when a user dies... what triggers a new fruit to be born? Or does a part of the previous owner transform into a fruit?

This would explain what Teach was doing... extracting the 'new fruit' from the body. But then one should appear from Ace too...