A good, glowing reference from a previous employer merely indicates that the person had a good rapport with their manager. A bad one, likewise, can indicate that there was a personality issue with the manager, and that doesn’t necessarily stem from the employee.

For instance, my previous manager found new employment after he’d gotten 2 formal warnings about his behaviour. However, if he hadn’t quit, I would have!
He did resign though, but before he did, he wrote an absolutely toxic review for both of his senior team members, and had his successor present, trying to poison the new manager. It didn’t work – and the review was subsequently dismissed as unfounded and unfair (as were the other reviews). But it taught me something about the legitimacy of references.

It might be a good idea for your company to reconsider whether it is protecting itself “from liability for a defamation lawsuit” with its name, rank, and serial number approach when providing references. Specifically, you should look into the emerging issue (in many states) of “negligent referral.” In some (perhaps many) instances, a “quick and easy reference” does not provide protection against a legal claim; it is more apt to do the opposite. If more employers were willing to be accurate with their references, reference checking would be more likely to be the valuable process that it has the potential to be.