NEW YORK - A judge should not delay Bernard Madoff's sentencing even though investigators have yet to determine how much money investors lost in the disgraced financier's multibillion-dollar Ponzi scheme, prosecutors said.

A fragmentary record of the activities of Madoff's firm, some of it going back as far as 1979 and on microfilm that needs to be digitized, has delayed efforts to identify each victim and losses, prosecutors said in court filings Friday in the Southern District of New York.

Reconstructing the record is likely to take several more months, but should not delay the 71-year-old's scheduled June 29 sentencing, they argued. They requested a 90-day extension beyond the sentencing date for the court to take up the issue of restitution.

Madoff pleaded guilty in March to charges that his investment advisory operation was a massive scheme to rip off investors.

The government and a trustee handling the liquidation of Madoff's business have been working to unravel the decades-long scheme so that assets can be recovered and redistributed, or restitution given.

Authorities so far have identified about 1,341 clients of Bernard L. Madoff Investment Securities, the court papers show. The known losses so far exceed $13 billion. Even with an extension, the prosecutors argued, it was unclear that the government and the trustee “will be able to reconstruct the documentary record and generate a list of all victims and corresponding victims.”