The Managers have an unspoken rule amongst themselves that they would never reveal their Disciple to one another unless necessary. This was because they didn't want their Disciples to know that there were other Managers and Disciples just like them.
In actuality, it all came down to the pride of the Managers. They wanted their Disciples to perceive them as someone above everything, and having others like them would downgrade their image.
However, with all the Disciples in close vicinity of each other, it's only a matter of time before they realize that there are other Disciples like them. Of course, there were already Disciples who were aware of such a fact, but there were those who were on the other end of the spectrum— those who had no idea that they were Disciples in the first place.
"You finally chose your Disciple, right? Is he joining the Official Beast Tournament?"
skadooosh~!