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The syn26050977_index_default index is “as-is” from just submitting the documents, the syn26050977_index_eng was instead configured to use as default analyzer the pre-configured English analyzer that includes an English stemmer (See https://www.elastic.co/guide/en/elasticsearch/reference/7.x/analysis-lang-analyzer.html#english-analyzer Note that this is the Elastic.co documentation as I could not find it in AWS or opendistro or opensearch docs).
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