If a Companion accepted Islam later and transmits a report apparently conflicting with one transmitted by an earlier Muslim, it does not follow that the later convert's report abrogates the other. The Companion might have heard the statement from an earlier Companion, or the actual time of the prophetic statement may be different from the date of the narrator's conversion.
The decisive question concerns the time of the ruling or event, not simply when its narrator entered Islam. Confusing these dates invites premature claims of abrogation.
An explicit, well-established report that the narrator personally heard a specified statement from the Prophet at a known later time can, however, provide chronological evidence.