G-14 was a project for standardizing all the different upgrades that were done to the 'default' G-6s. If you look at a very early G-6, you'll notice that it even looks quite different from the exterior, when compared to the later G-6s.
So, by 1944, the Luftwaffe had three prime objectives in 109 development;
1) develop a successor to the G series
2) when the new variant is finished, upgrade all existing G models to its standards
3) standardize all new G series production to 1) and 2) standards
1) would be the Kurfurst
2) would be the G-10
3) would be the G-14...
The problem was, the development for the Bf109K was delayed too much, thus the LW decided to carry on with 3) first.
Therefore, the G-14 actually arrived first, then the K-4, and the G-10 was the last mass produced 109.
IIRC, that is.. it was something like that.