When did Baldur's Gate's Outer City come to be?

Question

Last weekend I was re-reading the setting booklet from Murder in Baldur's Gate. Since the only game I have in this area is happening closer to the Year of Wild Magic than the Year of the Awakened Sleepers (or in less fancy terms: historically placed around when 3rd edition came out.) so far I've only read it for entertainment but it does give me quite a few ideas.

One important difference I have noticed is the mention of the Outer City - the area between the East gate (Basilisk Gate?) and Wyrm's crossing. Maps from Volo's Guide to the Sword Coast and the Forgotten Realms Interactive Atlas only show a handful of houses close to the gate.

So far I've assumed that the area simply grew in the 100+ years that have passed. Is that all there is to it? (I'm mainly looking for in-game information, in case it wasn't clear. But I consider the possibility that my premise is wrong.)

The Forgotten Realms wikia seems to agree. It shows both map versions and states that one of them (Volo's version) is simply for the Pre-Spellplague era while the newest (MiBG's version) is for the Post-Sundering era.

But there's an important issue at hand (especially for Rogue players): the local thieves' guild has a strong presence in the Outer city. This is IMO a big thing, especially with such an elite guard as the Iron Fist. If I understand correctly, at some point the area grew from being a handful of houses to a citadel in itself.

How and when did the Outer City grow so much?

For example: When would Little Calimshan have its walls constructed?

Was the Outer City already there for the most part, but nobody paid attention to it until recently?

Answer 1

I got an answer by Ed Greenwood (one of the authors of Murder in Baldur's Gate and... seriously, you should know who he is).

Here's what he had to say:

You've got it right: with the established part of Baldur's Gate CRAMMED into the bowl that descends to the river, and with the population of the city growing by leaps and bounds, and with a constant daily need for paddocks, stockyards, caravan assembly and encampment areas, and more warehouses, the part of Baldur's Gate outside the traditional walled area grew...and became the Outer City. It was already happening in the 1360s, but during the Spellplague "time jump," with magic in chaos and therefore "traditional" ways of doing things becoming more important and so more profitable, the growth of "the Gate" grew apace...and the only place it could grow was the Outer City.