The locus classicus to find these mismatches is a book called Shakespeare by Another Name, by Mark Anderson. (Full disclosure: I read the book pre-publication and am mentioned in it.) Ten years in the writing, Shakespeare by Another Name is almost 600 pages long, and a full third of those pages are footnotes. To take only a few of the shiny little details that appear in Shakespeare's Italian plays, Anderson mentions:
- Sailmaking in Bergamo, an inland city; long considered a gaffe, but this is correct
- Ttraveling from Verona to Milan, both inland cities, by boat; another "proof" that Shakespeare did not know Italy in detail, but this is also correct
- The nasal dialect of Padua
- Specific Italian phrases, such as "sound as a fish" and "by the ear"
- Features of Italian politics (e.g., Padua is under the protection of Venice, but Mantua is not) and of Italian law (e.g., the form of marriage between Katharine and Petruchio, which is Italian and not English)
- The seacoast of Bohemia, which did have a seacoast from 1575 to 1609
- The detailed geographic features of Ragusa (modern-day Dubrovnik), which is the "imaginary" city ofTwelfth Night (SBAN 85-87). Ragusa was the watering-stop for Venetian galleys; Oxford was reported to have injured his knee on a Venetian galley in the summer of 1575
- Giulio Romano's sculpture, which Shakespeare compares to Hermione's memorial statue; Romano's memorial statue to Castiglione's wife existed in Mantua (SBAN 97)
- A mural (also by Romano) in the main guest room of the Gonzagas' palace in Mantua (SBAN 97-98), similar to a mural described in The Rape of Lucrece
- A painting of the history of Venus and Adonis, in Titian's studio in Venice (SBAN 96), which shares elements with Shakespeare's Venus and Adonis
- References to the Jubilee of 1575; disguising herself as a Jubilee pilgrim, Helena's destination in Italy is "St. Jacques le Grand," Tuscan shrines to St. James the Great in Pistoia and Prato, used as overflow shrines during that Jubilee. (SBAN 100-101)
- "Friar Patrick's Cell," in Two Gentlemen of Verona, a real location in Milan where Friar Patrick O'Hely stayed in 1576 (SBAN 106)
Other little shiny details date the action of plays. In All's Well that Ends Well, for instance, it is casually mentioned that Don John of Austria is dead but William the Black Prince of Orange is still alive. That dates the action of the play between 1578 and 1584. The action of Hamlet takes place around November-December 1572--the star in the first scene, "that yond star that's westward from the pole" is Copernicus's nova, embodying the almost sacrilegious upheaval that forms the emotional core of the play. "The times are out of joint."
These details don't indicate the time of the writing of the plays. But they do indicate that, in the 1570s and probably in Italy, Shakespeare's immense creative imagination was gathering material, and picking up with that material the magpie facts that stud his plays.
And by "Shakespeare" I mean the man who wrote the plays. If he was gathering creative material in Italy in 1575-76, there does not seem to be a way that he could be William Shakespeare of Stratford.