It seems from the reply of a member, the avatars of Rama and Parasurama happened at the same time.
Further, when Parasurama avatar was partial, and the powers of Parasurama were transferred to Rama, then the total avatars of Vishnu would not be 10 and it is only 9 or between 9 and 10. How can you treat an avatar as complete when the role of an avatar was not full?
The Parasurama concept is not clear.
Since all these are fabricated stories, there was no need for any logical consistency. I am not sure whether Rama and Parasurama were born at, or near about the same time, but, in Valmiki's ramayana, Parashurama has an encounter with Rama when the latter returns to ayodhya after marriage to Sita. In that encounter Parashurama is made to be defeated by Rama. Thus, one avatar gets defeated by the next avatar!
If, therefore, Parashurama is reckoned as a half-avatar (nobody will take objection to this except the Bhumihar Brahmins, the Chitapavan brahmins, the Anavil Brahmins (Morarji Desai was one), Nambudiris and a few other castes, who hold Parashurama as their moolapurusha.), the same will apply to Balarama and so the total number of avatar strength will add up to 9, though the number of avatars will be ten only, something like the total marks scored by a student and the number of questions he attempted!
The half-avatars are not worshipped except in some remote corners.