about steam and pck files

I read on the Steam info pages that a pck file should be 1-2 GB max.
So, if you had a big game (10 GB) , that would mean you'd have to create several pck files.

So, I was wondering how you have to go about using them in your game code ?

As I'm developing the game, I have all assets in the res:// folder, and that's the path I would have to use to refer to them in my game code.
Once the game has been exported, the game code would have to refer to the assets in the different packs I assume ... So, how does that work ?

Thanks if you can shed some light ! =)

Megalomaniak Thanks !
Ok. That would explain why ... =)
But my problem is now : how.

I have seen the page you refer to (mods & dlc), but what I didn't understand is, is how that actually works for 'normal' pck's.
How can I use
var success = ProjectSettings.load_resource_pack("res://mod.pck")
while I'm still developing the game ?

Thanks for the help !
I'm still confused though ... =)