There was a time, not too long ago, when we thought we knew a great deal more about Beowulf than we do now. We knew that the poem, originally a work of oral composition, had first been written down in the seventh century and had been copied repeatedly until the final copy (our extant manuscript: British Library, Cotton, Vitellius, A.XV, ff. 94-209) was made sometime around 1000 AD. That particular manuscript, now known as the Nowell Codex, was the product of a single scriptorium, the work of two scribes, who included Beowulf in a single multi-text volume which emphasized monsters. In spite of the fact that the manuscript suffered in the dreadful fire at Ashburnham House in 1731, removing any trace of its binding or even of conjugation and thus leaving a stack of disjunct and deteriorating leaves, we have had little doubt as to the original structure and makeup of the codex before the fire. But now we are less sure of the date for the composition of the poem and some even question if it is the product of oral composition. The structure of the Nowell Codex has been examined anew and found to be far from self evident, and from this uncertainty about the integrity of the Nowell Codex has come a suggestion that the Beowulf portion is in fact a separate manuscript.
Clement, Richard W., "Scribal Practice in the Beowulf Manuscript" (2010). Library Faculty & Staff Publications. Paper 15.