The concern is that they may know what that unfunded pension liability is, but if that unfunded pension liability is going to be paid ahead of them in an insolvency, that obviously creates increased risk for their ability to be paid back, which means they're going to calculate that into the risk premium they charge, or they won't lend at all.
One of the other fears we have is if there actually is an unfunded pension liability and there is a superpriority for that, one of the potential strategic behaviours that might actually come from lenders is not to assert pressure on the company to fully fund their pension, which is what some people theoretically imagine would happen, especially since that often would mean that you'd be taking it out of working capital, but instead that those lenders will call their loans, and they'll call their loans early to ensure that they get paid, therefore putting the company into liquidation.