When learners can comprehend 98% or more of the tokens within a text, the lexical difficulty of the text is unlikely to inhibit reading comprehension (Schmitt et al., 2011). This phenomenon will be referred to as the Coverage Comprehension Model (CCM). The CCM is present in countless articles that describe the percentage of tokens necessary to comprehend reading materials (e.g., Nation, 2006). Further, numerous studies operationalize the CCM to provide evidence that participants were able to comprehend reading materials (e.g., Feng & Webb, 2020) by estimating: (1) the lexical difficulty of a text; and (2) the lexical mastery level of a learner. However, the validity with which the CCM is operationalized is limited by the following four assumptions: (1) 26 out of 30 words on a levels test is an appropriate threshold for mastery of a 1,000-word band; (2) the word counting unit used when estimating the lexical difficulty of a text and the lexical ability of a learner is appropriate for the target learners; (3) the item format used in levels tests can appropriately capture the type of vocabulary knowledge necessary when reading; and (4) the number of items on a vocabulary levels test accurately represents the difficulty of the 1,000-word band. This paper applies the findings of research to evaluate the validity of the first two assumptions, and concludes that the validity with which the CCM is operationalized in research is limited.