Provided are methods for sampling, testing and validating test lots, comprising: assembling a plurality of product portions from each of a plurality of test lots and combining the portions to provide a corresponding set of test lot samples; enriching the test lot samples; removing portions of each enriched sample, and combining the removed portions to provide a modular composite sample; and testing of the modular composite sample, and individual testing of the enriched test lot samples, using at least one suitable detection assay for a target microbe or organism, wherein when such testing is negative all test lots are validated, and wherein when such testing is positive with respect to the modular composite sample, or with respect to an individual enriched test lot sample, individual test lots may nonetheless yet be validated by further testing of a portion of respective initially-negative enriched test lot samples and obtaining negative results.