Do you have to see someone get saved for your witnessing to count?
No. A believer does not have to see the fruits of his witnessing or be the one who sees a person saved. One person sows the seed, another waters, and a third may add understanding, but God gives the increase.
Les teaches that the same principle Paul used applies today: you do not have to always see the fruits of your witnessing and testimony, and you do not have to be the one who sees a person saved. Paul planted, Apollos watered, but God brought about the increase. So one believer may sow the seed, someone else may come along and add to that person's understanding, and maybe even a third person will bring them a little further. Regardless of how many are involved in the salvation of an individual, God is the final cause, and God gives the increase.