Shadchan A proposed a shidduch. The couple met five times under the supervision of shadchan A. At this point one side requested that the shidduch be handled by shadchan B. The couple met twice more, and became engaged after the seventh meeting. Everyone knew that they would get engaged by the time they met the seventh time. How should the shadchanus gelt be divided between the two shadchanim.
Only the first shadchan, who proposed the idea and led it most of the way to completion, should be paid the shadchanus money. Although poskim make a division between a “matchil” and a “gomer” (one who “begins” and one who “completes” the shidduch), this division applies only when a second party takes over after the shidduch has for some reason stalled. In the case presented by the question, the shidduch did not stall, and there is no reason to think that it would not have been completed had the original shadchan not continued for the remaining dates. Therefore, the payment goes entirely to the original shadchan.
Sources: See Rema (Choshen Mishpat 87:39) and Biur Ha-Gra (117); Rema (Choshen Mishpat 185:10) and Biur Ha-Gra (13); Pischei Teshuvah (Choshen Mishpat 185:3).