I couldn't say for sure, but it appears to be a rebranding effort. We always had the label with just Glenfiddich 12, but lately I have seen the Special Reserve set in the same bins as the older 12. Special Reserve and new tins right next to the 12 and older designed tins.
I couldn't find anything on the net that differentiated them other than the "Toasted Oak 12" and the "Caoran 12". On Royal Mile's site, the Glenfiddich 12 has a picture of the newer tin and the Special Reserve on the bottle.