The 2005-2013 49L top case is similar, but different enough that the backrest pad won't fit.
The GTL backrest pad will fit on the 2014 RT 49L top case. It's the same top case as used on the K16GT, except for non-matched paint color. The RT 49L case is also available slightly cheaper without the central locking feature.
The K16GTL top case adds the taller, wider backrest and chrome rear trim. Those pieces are available separately from BMW, but you can't buy a complete GTL top case from them.
The GTL backrest pad will cost you just over $600, for just the pad and mounting hardware. And if you want the chrome trim, add $130, or add $240 with the LED tail light. And that's added to the almost $1,600 cost of the newer top case . . .
If you want a good quality, BMW-made 49L top case that'll fit your stock key, then the previous 2005-2013 case works well, and can be had used at decent prices.
If you want the central locking and the possibility to add the rear LED tail light bar, then the newer 49L top case works, albeit at a pretty high price, and not color matched to the bike.
But if you want all of the above at a decent savings over new, then PM me, as I have a pristine GTL 49L top case that will mount up and plug right into the RT . . .