Microsoft's strategy for launching Mango in various regions is a bit up in the air--in a lot of places it's up to the OEMs/carriers to roll out the update or release new devices.
If you go to this page: http://www.microsoft.com/taiwan/promo/wpmango/ You'll notice the big ol' "Coming soon on 9/9" which last we checked is today (in HK, tomorrow for us). The fan site We Love Windows Phone HK notes that marketing in Hong Kong and by assumption Taiwan, don't speak of dates or promotions unless that product has been launched already. Translation: this date could be the very same date that Microsoft begins to push out Mango--either by promotion or perhaps carriers.
On the other hand, this could be an older page, dates could have changed, etc. We do know that Mango is close for a lot of folks and this is clearly one more indication.
update: And like all things too good to be true, this looks to be a misunderstanding. Evidently there were two promotional events for Mango launched by MSTW and neither is the actual launch.