Borrowers have defaulted on billions of dollars in private student loan debt. Seeking payment on those soured loans, creditors file tens of thousands of lawsuits each year.

But those lawsuits often contain legal and factual errors, according to borrowers’ lawyers — and a growing number of judges have upheld their arguments and rejected creditors’ claims.

Below are five defenses that have been successfully used to halt student loan collection cases.

The creditor cannot prove that it owns the debt.

Many private student loans are transferred by their original lender to investors through a process called securitization, in which thousands of loans are pooled together and sold as a package.

But proving that the chain of title remained intact through every ownership transfer can be a challenge for debt holders. In one frequently cited ruling, Lovett v. National Collegiate Student Loan Trust 2004-1, a Florida appeals court held that the creditor, a securitized investment trust, had not submitted sufficient evidence to prove that it owned the note on a loan originated by Bank One in Chicago.