The late-acquired French subjunctive–indicative contrast conveys important information about event realization and is characterized by bound morphology, form ambiguity, contextual restrictedness, and the infrequency of the subjunctive. This study contributes underrepresented adverbial-clause interpretation data and incorporates lexical effects to extend what is known about why French mood is late-acquired. We assess interpretation of four adverbial conjunctions which primarily co-occur with subjunctive or indicative mood in corpus searches. Analysis of 77 participants revealed a statistically significant interaction between mood and proficiency, with more proficient learners affected by mood, whereas clause order influenced less proficient learners. Moreover, lower-proficiency learners treated adverbs within a particular class of co-occurrence more similarly across the 32 items than our advanced learners or native speakers, who were sensitive to lexical effects, attributable to the roles of frequency and semantics. The study contributes to the growing body of research on late-acquired structures, for which learners attend to evolving cues across acquisitional trajectories.