This study investigates the influence of semantic maturation on early lexical development by examining the impact of contextual diversity--known to influence semantic development--on word promotion from receptive to productive vocabularies (i.e., comprehension-expression gap). Study 1 compares the vocabularies of 3685 American-English-speaking typical talkers (TTs) and late talkers (LTs; 16-30 months old; 1257 females, 1021 gender unknown; ethnicity unknown; data downloaded in 2018) and finds that LTs, with a longer preverbal phase, produced nouns with lower contextual diversity (R[superscript 2] = 0.80), but verbs with higher contextual diversity (R[superscript 2] = 0.13). Study 2 compares computational network growth models of semantic maturation and finds that verbs require more semantic maturation than nouns, and TTs produce words that are more semantically mature than LTs.