Mexico City:

In 1941, the General Anaya borough was merged to the Central Department, which was then renamed "Mexico City" (thus reviving the name, but not the autonomous municipality). From 1941 to 1970, the Federal District comprised twelve delegaciones and Mexico City. In 1970 Mexico City was split into four different delegaciones: Cuauhtémoc, Miguel Hidalgo, Venustiano Carranza and Benito Juárez, increasing the number of delegaciones to sixteen. Since then, in a de facto manner, the whole Federal District, whose delegaciones had by then almost formed a single urban area, began to be considered a synonym of Mexico City.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When was the General Anaya borough officially merged into Mexico City?
1941