Do corpus data offer us clear insight into how native speakers perceive and use forms that are said to be stylistically circumscribed? We examine two features from Czech verbal morphology, contrasting their description in grammars with findings from the Czech National Corpus. We then test whether corpus frequency is predictive of usage and evaluation through experiments in which native speakers rated and completed forms in sentence-long contexts. The results show that corpus frequency is a good predictor, while the stylistic differentiation between these forms proves complex to assess in studies of this type