When St. John gives Jane Sir Walter Scott’s Marmion, and Jane-the-narrator
comments that this was a new book, it seems as if Brontë is providing
a definitive statement about when the events of the novel take place,
since Marmion was first published in 1808.
However, other characters in Jane Eyre refer to
books published after this date. Blanche Ingram, for instance, refers
to Byron’s poem The Corsair in Chapter 33,
but Byron’s book wasn’t published until 1814.
Brontë was obviously not especially concerned with fixing her story
in a precise and consistent relation to historical dates, and perhaps
she selected the texts mentioned in her novel for other reasons.