Translatability of Catallus

Last week, there were two Latin teachers here for dinner (sadly, a rare occasion). They both said that a significant part of the English translations of Catullus is guess-work, because the meanings of some of the vernacular metaphors used in his poems are no longer certainly known. Also, to a far lesser degree, certain Catullan metaphors will not even be recognized as metaphors. Is this true--I have no reason to think they'd be making this up--and, if it's true, how common a problem is this for translators of other Latin writers?