Based on the information you provided, you should inform the XXX Partnership that you claimed (utilized) the losses and wait for their response. Based on their decision, you will know whether an amended return is necessary (or even possible) or if you can report the correction in a current year.
If they issue a correction that results in additional tax for a prior year, it is unlikely that you will be assessed any penalties since the error was not of your making. If penalties are assessed you can appeal them.
Interest is likely to be charged, but not at a punitive rate. The IRS pays taxpayers interest on late-arriving refunds, so they charge interest when they get tax payments later than expected.
You are right to question whether they will allocate the correction to the current year or a prior year. Once they make that decision, they should provide you with the necessary tax form (K-1) to report the correction.
