Hello @praveen.rangaiah0 ,

To address your question, we have confirmed that "the key information is retrieved from the source as part of Tick History HistoricalSearch which is assigned to an instrument and this will not get changed."

Hope this information helps

Hello @praveen.rangaiah0 ,

HistoricalSearch result keys are unique:

https://selectapi.datascope.refinitiv.com/RestApi.Help/Context/Operation?ctx=Search&opn=HistoricalSearch#

From HistoricalSearch request you can also confirm, when each of the instruments that are found by the search are/were valid:

{
                {protocol}}{
                {host}}{
                {api}}Search/HistoricalSearch
{
  "Request": {
    "Identifier": "0#bl2:",
    "IdentifierType": "ChainRIC",
    "Range": {
      "Start": "1996-01-01T00:00:00.000Z",
      "End": "2021-12-31T00:00:00.000Z"
    }
  }
}

Resulting in:

"@odata.context": "https://selectapi.datascope.refinitiv.com/RestApi/v1/$metadata#Collection(DataScope.Select.Api.Search.HistoricalSearchResult)",
    "value": [
        {
            "Identifier": "0#BL2:",
            "IdentifierType": "ChainRIC",
            "Source": "",
            "Key": "VjF8MHgzMDAwMDAwMDAwMDAwMDAwfDB4MzAwMDAwMDAwMDAwMDAwMHx8fHx8fHwwI0JMMjp8",
            "Description": "Historical Chain",
            "InstrumentType": "Unknown",
            "Status": "Valid",
            "DomainCode": "6",
            "FirstDate": "1998-02-03T00:00:00.000Z",
            "LastDate": "2021-11-14T00:00:00.000Z",
            "History": []
        },
        {
            "Identifier": "0#bl2:",
            "IdentifierType": "ChainRIC",
            "Source": "",
            "Key": "VjF8MHgzMDAwMDAwMDAwMDAwMDAwfDB4MzAwMDAwMDAwMDAwMDAwMHx8fHx8fHwwI2JsMjp8",
            "Description": "Historical Chain",
            "InstrumentType": "Unknown",
            "Status": "Valid",
            "DomainCode": "6",
            "FirstDate": "1998-12-04T00:00:00.000Z",
            "LastDate": "2000-09-02T00:00:00.000Z",
            "History": []
        }
    ]
}

Therefore, these keys can always be used to distinguish between the results returned by the HistoricalSearch request.

The part of your question of whether the keys are guaranteed to stay the same for the same instrument, or ever update, we am going to research further and get back to you on.