Thank you for your comment João :-)

Let's see if I can clear the misunderstanding.

{quote:jff}
   If you edit E, why would you get a different entry E'? And shouldn't entries with different versions considered different entries? 
{quote}

If you see the model you'll notice there is a composite pattern applied in the __Entry__ object, where is said it represents the historic. That means when you edit an entry E, you're actually creating a new one E' related with the previous where the only different is a higher version number and the information changed due to edition. 

{quote:jff}
And what happens if tags change from version for version?
{quote}

I'm not considering such scenario. Mainly because I think that what really matters are the tags for your current content, not from some in the historic. Plus I also don't think the tags will change along an __Entry__ history, most probably they'll stay the same or at most probably some will be added.\\
Of course I may be wrong.