During one of the sales in 2016 I ordered a Mk4 rail - invoice has it listed as 13", and putting a tape measure on it, it's 13" on the dot from tip to toe.
Looking now on the G website and other vendors, even though the part number is the same (05-278B), the rail's now listed as 13.5".
Did the rail actually grow half an inch, or did the nomenclature change and it's still physically 13" long? All other things being equal, I'm hoping it actually gained half an inch in length...a new one would fit what I'm currently building, better