> This is not always the case.
I did not say it was always the case. I said "plenty of", not "every".
Life and politics are complicated, and I left plenty of room in my original statement for nuance and counter examples, please do not remove that for me.
> There was a time when IS had control of a significant unchanging area of land
Unchanging is not the same as uncontested, and I'd argue that IS never had an "unchanging" area of land. Every square foot of IS territory was actively contested, and if you look at the map of its territory over time it moves and shifts and is full of uncontrolled pockets. The nice, clean maps of IS territory on the news were in fact simplifications for easy public consumption. The real situation on the ground was always much more fluid and complex than that. If you look at a map[0] of the actual territory that IS controlled, it is pretty far from the necessary boundaries to run a state. Put bluntly, this is a battle map, not the kind of map that you can make a state out of.
Even the areas that IS held, it did not hold for very long or very securely. Take Tikrit, for example, which IS only held from June 2014 to March 2015, with forces massing for the attack in February. It's hard to argue that a group holds "unchanging" territory when major cities are changing hands every 10 months or so. Furthermore, if an opposing force is able to mass an army outside your city and put siege to it, you are very far away from having "sufficient ability to defend their borders". Given that IS' territorial claims collapsed rather quickly, I think that assertion is pretty good.
> Hence being referred to as “so-called Islamic State” most of the time in news broadcasts.
Right, because the war was still on, IS was still trying to seize the land and fortify the borders of what they hoped would eventually be their state. If IS had won or fought the battle to a draw, I have no doubt that they would have gotten roughly the same level of international recognition that say, North Korea gets and they'd stop being "so called". But they didn't do that, so they never stopped being "so called".
Really, the counter example you should have gone for here is Haiti. Haiti unquestionably was capable of defending its borders, and in fact repelled several attempts to retake the island. It also did not get recognized for nearly 20 years by basically anyone until they agreed to reimburse France for the loss of their property, including distastefully the value of the slaves who were now free. While plenty of states get recognized once they manage to successfully hold and defend territory, not every state gets recognized that way. Sometimes other factors dominate, such as the fear of other slave holding states in recognizing the independence of a country created via a slave revolt.
0 - https://en.wikipedia.org/wiki/Islamic_State#/media/File:Near...