To fully understand the complexities of the Anglo Saxon Chronicles is outside of the remit of this site, although for those interested in learning more Wikipedia is a good start.
For this brief explanation of the ASCs in relation to Brunanburh I have leaned on Alistair Campbell’s ‘The Battle of Brunanburh’, a book which focuses on the Poem as found in ASC MS A&B in tenth century hands and MS C&D which are believed to be in an eleventh century hand. MS E we will look at separately.
MS A – This is believed to be, or be a copy of, a chronicle created in the time of Alfred the Great and maintained until 891. A number of different scribes are believed to updated the document until 924, sourcing the information from other chronicles. Another continuation occurred from 925 until 975, and this includes the Brunanburh poem as usually quoted. The chronicle received further continuations until 1001. MS A calls the battle Brunanburh, although someone later added an ‘n’ above the first ‘n’ of the word. Brunanburh remains the accepted version.
MS B is beleived to be a copy of a chronicile copied from MS A until 891, then added too accordinaly in line with MS A. MS B ends in 977. MS B calls the battle Brunnanburh.
MS C is as MS B but was continued to 1066. This calls the battle Brunnanburh.
Another copy of the 891 chronicle was sent to the north of England and formed the basis for another set of chronicles from which were copied MS D & E. MS D calls the battle Brunanburh, while E, which omits the poem, calls the battle (in a northern tradition?) Brunanbyrig.