Whether you are referring to the Reports/TrialBalance endpoint in the Accounting API or the FinancialStatements/TrialBalance endpoint in the Finance API, you are correct in that this only returns data for a specific date (as documented on the developer portal here and here).

Although the Xero product itself allows you to produce a report that shows multiple comparison periods, this isn't directly possible through the API with a single call. If you want to achieve a similar result through the API then you need to call the trial balance report end point multiple times with the required dates, then stitch together the results yourself.