Why is Chiisaku Natta Meitantei considered the "real" first episode? MyAnimeList has published a database entry for Detective Conan: Episode One - Chiisaku Natta Meitantei.

In this entry, the synopsis reads:


  The "real" episode 1 of Detective Conan written by the Mangaka Gosho Aoyama.


What makes this episode the "real" first episode? Was the story in the original first episode not by the mangaka?
That is a two-hour remake of the original 1st episode, in celebration of the anime celebrating 20 years in broadcast. The special retells what happened on the day Shinichi’s was transformed into the body of a child. The special includes new scenes that weren't in the original manga or the first anime episode. 

https://www.youtube.com/watch?v=T_g9zHvMXBQ