Both HSIM8 and 1YMH9 are historical RIC. You may need to set the "AllowHistoricalInstruments":true in the ValidationOptions of request body. Below is the sample.
"IdentifierList": { "@odata.type": "#ThomsonReuters.Dss.Api.Extractions.ExtractionRequests.InstrumentIdentifierList", "InstrumentIdentifiers": ..., "ValidationOptions": { "AllowHistoricalInstruments": true }, "UseUserPreferencesForValidationOptions": false }