Factual errors and felicitous variants

I've discovered that one of the poems in my book contains a factual error. It irks me, but I don't want to correct it, because I like the line.

William Empson's poem 'Invitation to Juno' contained a factual error in its early versions. It's the usual exquisite tortured cleverness about unworthy man wooing aloof woman, and the last stanza reads:

Courage. Weren't strips of heart culture seen
Of late mating two periodicities?
Did not Professor Charles Darwin
Graft annual upon perennial trees?

The trouble is, Darwin was never a professor. In later versions Empson substituted the much inferior line 'Did not once the adroit Darwin', correcting the error but weakening the verse (that horrible metrical filler 'the adroit' doesn't even sound right).

This in turn reminds me of a Marvell eclogue I read recently, 'A Dialogue between Thyrsis and Dorinda', where, in the passage where Thyrsis describes paradise -

Oh, there's neither hope nor fear,
There's no wolf, no fox, no bear.
No need of dog to fetch our stray,
Our Lightfoot we may give away...

- some manuscripts have the line 'Free from the wolf and horrid bear', which strikes me as a far classier one than the main reading.