I spent months fighting a claim for mesalamine DR tablets (and getting nowhere) only to discover that the insurance personnel were treating it as a different claim for mesalamine EC capsules—a totally distinct formulation. Any doctor or pharmacist could tell you that they're not equivalent. But they had different approval criteria in the insurance system, and even though I met the criteria for the former (the drug I wanted) they kept denying me for not meeting the criteria of the latter (the drug I did not want).
But those are both oral forms. I think if they'd tried to run the claim as the suppository version, the error would've been more obvious.