I do not know. And I have no real first person information on Syria except for one friend who is half Syrian who has some family in Homs[1]. However I'm dubious about the 300,000 number since it just seems to be reflexively repeated for years. And because sounds like the number of people escaping Eastern Aleppo is a small trickle. Despite that it's barely a functioning city at this point.
Also there is this.
> While aid groups estimate anywhere from 175,000 to 300,000 people still live in eastern rebel-held Aleppo, it is difficult to gauge the accuracy of figures from rebel territory. For example, Darayya, another besieged rebel-held city, was said to have more than 8,000 occupants. But last week, when government forces evacuated the entire town, they found fewer than 2,000 people still residing there.
Also there is this.
> While aid groups estimate anywhere from 175,000 to 300,000 people still live in eastern rebel-held Aleppo, it is difficult to gauge the accuracy of figures from rebel territory. For example, Darayya, another besieged rebel-held city, was said to have more than 8,000 occupants. But last week, when government forces evacuated the entire town, they found fewer than 2,000 people still residing there.
http://www.latimes.com/world/middleeast/la-fg-syria-aleppo-m...
[1] And she of course knows little