Navient Corp. is challenging assertions in a securities class action that top executives at the Wilmington-based Sallie Mae spin-off knew the firm was underreporting to investors the number of delinquent accounts in its student loan portfolio.

Attorneys for the company argued in a court filing this week that a class of investors had based their allegations on the accounts of four “low-level collection personnel” with no access to senior management, as Navient wrapped up briefing on its second attempt to escape a securities suit that has followed the firm for more than two years.