The NCIS franchise is a massive institution, so its no wonder some actors have played multiple characters within its expansive storyline. It would throw off the narrative in most television shows to have the same person appear as different characters, with many only running for a few years. However, NCIS rich tapestry of more than two decades on television allows actors to weave in and out of the narrative as different NCIS characters seamlessly. Moreover, the fact that NCIS has so many spinoffs means some actors can always show up on a different show as a new character.

https://screenrant.com/ncis-actors-different-characters-play/