Pile of User Stories: how to organize and contextualize em?

Here is a scenario that I already dealt with in different teams:

A pile of user stories that mention different functionalities and features! We don’t have any overview or grouping of each. The sprints were passed by and no one took care in organizing all this stuff. So later on, the team plans to organize these stories by groups of features in a very late sprint, getting into this very nice result:

Still this is not enough because a new team member arrives, take a look in some screens of the application and asks the million dollar question: what does the feature <insert feature name here> do?
Will the team stop to explain to the new colleague and dig into the group of user stories, read, contextualize, interpret and finally, summarize them?

So… Is there a way in which we can have an overview of what does this feature do and which are the possible flows that exists in it?

Then we back in time!!! UML activity diagram (or the much earlier, the fluxogram/flowchart) to the rescue!

I still don’t know a better way to overview, to document and explain a feature to someone. Flows are graphic, very visual and shows in a simple fashion the possibilities that this feature have. Just looking at the flow we can check if that functionality is simple or complex. Reading the flow you quickly see the ins and outs from that feature. And here is the best: we do this without the need of reading repetitive user stories cards, merging and re-contextualizing em.

What we do here is when we receive a new user story, we check which feature is and in case of an already existing user story that references to the same story, we update our UML model with an activity diagram that will serve as documentation and evolution of this feature!
And this is working extremely well in all teams that started to work this way. Now the teams get:

• an overview of a feature described in a graphical manner, useful to show to incoming colleagues and clients;
• a way to check the evolution of a feature;
• a document to verify and discuss if this new incoming user story fits nicely into the feature and the impacts it can cause.

I don’t know if this is the best way to deal with this question. So let me know! How do you deal with a big quantity of user stories and how do you group and contextualize em in a way that is easy to check what a feature do?

Pictures were took from Hawkexpress and IBM.