How much do you think learners retain after 6 months of attending a program, provided the skill learnt is part of their monthly job tasks?

Firstly, we have to remember that the retention of any theoretical aspect gradually diminishes with the passage time. But, we may retain maximum provided its application part is practical. Therefore, I believe that the learners will retain at least50% of acquired knowledge provided the skill learnt is part of their monthly job tasks after6 months.