Okay, this may be super-nitpicky and make me sound like a prat, but the GECK does not contain any data. The GECK merely reads the game data from the .esm and .esp files you provide it with.
You are, of course, entirely correct. Well except for some base effects and their archetype and defaults which are in the GECK not the .esm files for FO:NV, if I recall correctly, because even if you were to write an .esm from scratch they'd still be there. The difference is probably lost on someone that doesn't know what TESCS and GECK are.
So let me amend my statement:
The GECK is an editor that allows you to open up the archive files of FO:NV (as well as FO3) as well as your own files and use them as a construction set to recode, change, modify or add to the base game up to and including your own quests, zones, NPCs, items, effects, ect.
If it's in the game it can be made with the GECK and between the GECK and FOSE you can do things that the designers never even thought of.
And my original statement still stands, you could rebuild almost all of FO:NV from the ground up using just the geck, some 3d modeling software and a sound recorder program.