Which Rick Steves book is more up to date?

That is probably the answer. Just look at the publishing date to see which one is more recent.

Try to get the Rick Steves Europe staff to answer this question. They're the experts on their own books.
They usually monitor this forum during regular business hours, so maybe check back here tomorrow.

Thanks Frank, but that is not the answer. Both give the same 2014 publication date.

And yes, Kent, I was hoping for a reply from Rick Steves Staff.

Italy 2015:
https://store.ricksteves.com/shop/p/italy-guidebook
Specifications: Oct 2014 publication date

Best 2015:
https://store.ricksteves.com/shop/p/best-europe-guidebook

Specifications: Aug 2014 publication date

As a guess data coiuild be half a year old at time of publication.

Rick Steves does post updates for major real time changes:
https://www.ricksteves.com/europe/guidebook-updates

E.g. Best

Cinque Terre Riomaggiore La Lanterna restaurant has closed. For books
printed before October 2014, the following may apply:

Riomaggiore Riomaggiore Reservations no longer runs a hostel in
Riomaggiore.

Vernazza You can now store your bags at the gift shop in Vernazza’s
train station (April–Oct daily 8:00–20:00, closed Nov–March).

Ristorante Belforte’s antipasto misto di pesce is €18 per person for
five plates, and is for a minimum of two people.

The publication dates are pointing you in the right direction - the Italy book is more up-to-date. Because Best of Europe incorporates information from 8 other books, it's actually the last book of the 2014 cycle. Anything dropped from the Italy book was dropped for a reason, which could be closure, price changes, customer feedback, finding a place that we liked better, or even a request from the business owner.

Thank you..

On the back cover of most Rick Steves guides, just above the bar code and ISBN, you can see the month and year the guide was published (inside the book on the almost-back page, you only see the year).