How do The Book of the Dun Cow and The Book of Leinster preserve early Irish saga material?

The Book of the Dun Cow (Lebor na hUidre) and The Book of Leinster are vital codices that preserved early Irish saga material, which had been transmitted through oral tradition and earlier, now-lost manuscripts.12

• The Book of the Dun Cow: Compiled around 1100 at the monastery of Clonmacnoise, this is the oldest surviving miscellaneous manuscript in Irish literature. It preserves older treatments of saga material than those found in The Book of Leinster. It contains significant portions of the Ulster cycle, including a partial text of The Cattle Raid of Cooley, alongside historical accounts and romantic sagas.12
• The Book of Leinster: Written in the mid-12th century, this manuscript serves as a major repository for the secular literature and historical traditions of Ireland. While it contains later versions of some sagas, it remains a crucial source for reconstructing the social history, genealogies, and heroic narratives of early Ireland.23

Together, these manuscripts captured a picture of a hierarchical warrior society—including details on chariot warfare and social taboos—that is otherwise poorly documented in historical sources.2