This is episode is listed as being broadcasted on September 28, 1996 on IMDB and on October 19, 1996 on Wikipedia.

Do you have an official proof of its original airdate ?

Huh, I did not now that. I checked the reference for the episode on wikipedia and that had the date as October 19, 1996 as well, so I thought that would be enough.

I tried searching but couldn't find an official proof. But, just to check when the date was changed on wikipedia, I dug through the page history and the change was made all the way back in 2008 with only the following link attached: http://forums.toonzone.net/showthread.php?t=220162, a forum which has since closed.

I googled the link to see if it had been referenced anywhere just to check and it led me to the forum of site animesuperhero.com. Searching the forum, for this particular episode, led me to a post from November 2008, detailing how and why the date discrepancy is present.

Well, that's all that I could find regarding it. Hope it helps.