Not all permutations are issued as "standard issue" stamped plates and some states have a format where there wouldn't be any confusion about where number and a letter would be. Customized plates might have a chance but they're free to refuse to issue any plate they want and if there's an issued customized plate with any ambiguity in the OCR, they can just run through all the permutations and match it against secondary values like color, make and model or the registered owner's address. The odds of two people with a late model red Chevy truck living in the same areas of the state with similar travel routes, one with something like 'O0O0NMN' and the other with '0O0OMNM' is probably astronomically low.
I would be more worried about a false positive in the OCR. Say your plate is 0000000 and someone steals a car with plate OOOOOOO and commits a crime. Now you get pulled over and have to deal with the police.