That was secret transmission. Ma Jo Zen Master got transmission from Pai Chang in a big public ceremony. That's a famous story. It's possible for you to teach other people. Inka means many Zen Masters are possible.
Transmission means only one Zen Master.
Inka and transmission are different. This title has almost disappeared in Korea, although it still exists in China. Now we have the Ji Do Poep Sa Nim ceremony, which is very important. In this ceremony we come together and believe him or her. If the Zen Master gives inka or transmission only privately to this person, sometimes the other students don't understand.