To a measure, it is not subject to interpretation, however, when you ask them to look up the case law, you are asking them to make an interpretation. Not only that, it is not incumbent on law enforcement officers to look up case law or statute law on demand on the spot. (I can see it now. "No, officer, you can't exercise that search warrant. You have to look up the law before you come in here," all while drugs are being flushed down the toilet and the dealer heads out the back with the guns in hand)
If ignorance of the law is no excuse for me, then why does it excuse him?
I did not say anything of "ignorance" of the law. I said that he did not have to understand each interpretation of the law. Otherwise, each and every lawyer that cops stop can get out of each and every violation of the law, simply by knowing how to word their demand for the officer to "follow the letter" as they see it.
The letter of the law in Ohio says that they should follow the Michigan statute. And to follow that to it's ultimate end, OHIO police officers will not have MICHIGAN case or statute law in front of them to read, let alone interpret.
What should they do at that point, take the word of the person who they've stopped? No! At that point, they would have to rely upon what they know. That's where the judge gets involved. And again, going back to your initial argument, you stepped out on that fringe, you have to defend your decisions to act in that fashion, especially when they skirt the laws of one state versus another.