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Studies documenting Human-Induced Rapid Evolutionary Change (HIREC) routinely compare contemporary allele or morph frequency distributions with historical baselines. All too often, this involves the re-sampling of a population that was sampled at a single time point in the past. However, year-to-year fluctuations in magnitude and direction of evolutionary response may make such studies prone to erroneous conclusions, where long-term evolutionary trends are inferred from what in fact are short-term fluctuations. Here, we explore this problem by re-sampling three Dutch populations of the land snail Cepaea nemoralis, whose shell colour polymorphism is known to be under thermal and predatory selection. Each of these three populations was originally sampled in at least two different years in the past. We show that conclusions on evolutionary change are strongly dependent on which of the historical sample dates is used for comparison with the contemporary sample. Our study highlights the fact that year-to-year variation in allele frequencies may often be so strong that a simple two-point comparison is unreliable to detect long-term evolutionary trends.