So this is a two parter: First, is there anything in the lore that tells us where/when the Sheild Dwarves and Gold Dwarves split as racial entities? The Second part is: Where do the dwarf subraces originate as a matter of game design? Were they Ed creations or were they appended later? Thanks in advance.
How can life be so bountiful, providing such sublime rewards for mediocrity? -Umberto Ecco
Re: the first... Shield Dwarves and Gold Dwarves have been isolated from each other for 12,000 years in different physical and political circumstances. 3e's Races of Faerûn, FR11 Dwarves Deep -- it's the main Realms reference for dwarves, and the 2e The Wyrmskull Throne modules are the best sources for this kind of lore. "Elminster Speaks: Khôltar" [on the Wizards site] is useful also.
With respect to the second, I'd imagine only Ed could tackle that to any specific and elaborate degree.