Although some are under the impression that there are international treaties which define the status in Constantinople, nothing is further than the truth, as there was nothing specific that occurred after the fall in 1453.
The misconceptions regarding the 1923 Lausanne Treaty, or even the 1920 Treaty of Sevres, are not valid, and have not brought any change whatsoever.
As a matter of fact, at the end of the Byzantine Empire and according to the data of the era, there was no agreement regarding Constantinople.
Following the war, the siege and then the fall, a procedure came to an end without ever resulting to an agreement.
Consequently, those who argue that the position of Constantinople falls under a certain institution, and especially at an international level, are merely ignorant, and are influenced by the associated propaganda and misinformation.
Additionally, a zone which is within the occupied Thrace, and which has a direct point of contact with Constantinople, functions in exactly the same manner, because the buffer zone which appeared in the Lausanne Treaty, and which, as far as the borders were concerned followed the Sevres Treaty, does not include Constantinople itself as such.
But it is quite interesting of course, especially in the strategic context, that it was selected even though it was not related to the Catastrophe of Asia Minor.
Because, even according to then given data, they understood in the East that this regarded a vulnerable point, since it couldn’t be supported directly via Thrace.
Therefore, they ensured the neutrality of the region, because they simply didn’t know how the strategic schemes would’ve developed in subsequent periods.