AMD's Senior Product Manager, James Prior talked a bit about the story that broke earlier on last week related to the fact that Threadripper is fitted with four AMD Zepplin dies. He mentions that the two extra dies have "no path to operation".

That also means you cannot activate 32-cores of course and that EPYC is a different processor (but sharing the same design). Prior outted his remarks on twitter:

Threadripper is not a Epyc processor. Different substrate, different dies. 2 dies work, other 2 have no path to operation. Basically rocks.

Prior also added that AMD decided to use the term "dummy" instead of "inactive" to describe Threadripper's additional dies as there is no way of utilizing/activating these additional CPU dies.

Yes, exactly why they're not described as inactive, but dummy. Doesn't matter if they were dead, or active, they're not going to work.

Earlier on overclocker der8auer tried to de-lid a Threadripper, but with the heatspreader soldered to the dies he broke that CPU (of course). In his video he took it a step further and check out the dummy dies. When he pealed them loose, the four dies revealed themselves, opposed to some sort of two die / two dummy configuration. James Prior however still has not mentioned as to why exactly they are using two extra dies? But likely, the ones used did not pass wafer inspections, e.g. they are non working dead and thus re-used

AMD James Prior Sheds Light on Threadripper Dummy Dies