The scripting API method call: get_date() provides the ability to retrieve historical data using a date range as an optional parameter specification. The following request will return valid rows of data.
df,err = tr.get_data('.SPX', ['TR.PriceClose'], parameters={'SDate':'1970-01-01','EDate':'1970-01-04'})
When going back further in time, it appears for the above requested instrument, the data is available only until Jan 1, 1970. This can be further observed when requesting for the same data years earlier.
The above request doesn't have any historical data for the date range specified. Although it returns one row with a NaN as the value, I'm assuming this implies no data. However, I would expect such a result to occur if I continue to go back in time. Instead, if I continue to go back in years, I can reach a point where my specified date results in an exception being thrown.
I would expect no data to be returned, or something similar to the above request. Not an exception.