I'd say you're right. Penguin was first released on April 24 - see this discussion [webmasterworld.com]
There has been one and only one Data Refresh for Penguin and no algorithm change. The data refresh was on May 26 - that Penguin Refresh discussion is here [webmasterworld.com] No one one in that discussion reported a recovery.
My take on Penguin is that it is another "sub-algorithm" based on machine-learning, just as Panda was. That means any recovery can only happen when Penguin is re-run or at least has a data refresh.
I've read some reports around the rest of the web that claim some Penguin recovery. However I have never been convinced that Penguin problem was the correct diagnosis in any of those cases. Either the date of the supposed "problem" did not coincide with Penguin or its recovery did not coincide with the one Penguin Refresh.