Yes, that's the most likely period to finally add it in....probably just before or just after the War of the Pacific though, would have to check for some more data.
Still, as mentioned before, there could easily be earlier periods where the culture is added for a few years, and then removed again, then given again after a decade or two, etc.
And there could still exist an "optional" event (using flags, if I code it correctly), all the way through, that may give the culture back permanently if the player/AI is truly a benefactor of the natives and integrates them into society....of course, such a thing would be rather expensive and would upset the upper classes.
Still, as mentioned before, there could easily be earlier periods where the culture is added for a few years, and then removed again, then given again after a decade or two, etc.
And there could still exist an "optional" event (using flags, if I code it correctly), all the way through, that may give the culture back permanently if the player/AI is truly a benefactor of the natives and integrates them into society....of course, such a thing would be rather expensive and would upset the upper classes.