This is an official BMW chart that was leaked.
The columns list the model code, model trims, the start of production month, the end of production month, the number of months of production (for the 2014 model year cars), and the manufacturing plant location.
As you can see, the 428i coupe, 428xi coupe, 435i coupe, and 435xi coupe are confirmed. The 4-series coupes will begin production in July 2013 in Munich.
The 428i convertible and 435i convertible are confirmed as well. The 4-series convertibles will begin production in November 2013 in Regensburg.