This paper investigates the methodological discrepancies underlying the measurement of adult learning and education (ALE) participation in the UK by focusing on four major surveys -- APiL, PIAAC, AES, and LFS. Grounded in the Total Survey Error (TSE) framework, we systematically examined the surveys' documentation and compared their definitions, reference periods, and operationalisation of ALE. Our review identified significant inconsistencies, including mismatched age ranges, divergent weighting schemes, and ambiguous question phrasing. These methodological differences potentially undermine data validity and complicate cross-survey comparisons. As a result, policymakers and researchers may be left with an uncertain evidence base for shaping adult education policies. To address these issues, we propose two scenarios: first, conducting qualitative interviews to refine how participation questions are conceptualised by adults, and second, implementing survey experiments to assess the effects of various reference periods, data collection modes, and question formats on reported participation rates. We suggest that strengthening the methodological foundations of ALE surveys can foster greater confidence in the reliability of adult education statistics, informing more nuanced policy interventions and advancing future research directions.