I believe that Hannah probably offered only a single bull (as in the Septuagint and 4QSama); supporting this choice is the next verse in the Masoretic Text which speaks about “the bull.” I believe the Masoretic Text was textually corrupted when the continuous writing (without spaces between words) of the original wordsprm/shlshh (literally: “bulls three”) underlying the Septuagint was divided wrongly to pr mshlsh (“three-year-old bull”).
Tov uses the Dead Sea Scrolls to elucidate the original language of the Bible not only because they are the oldest Bible manuscripts, but also because they provide additional logical clues. He concludes: “In finding our way in the labyrinth of textual sources of the Bible, we must slowly accumulate experience and intuition. When maneuvering among the sources, we will find much help in the Dead Sea Scrolls. But they must be used judiciously.”