The problem with the online decoders is that the couple that are out there are pretty simple. Basically they’re just comparing the input to a fixed list of codes they were programmed with.
It wouldn’t be all that difficult to put additional rules into a decoder like that, you could check for alpha numeric order with a single line of code and have the decoder kick it out with an error message. You could input additional code to check the year and model of the car against the body codes, since different years and models used the same code for different options. So you could have a list of options for each body code that would be checked against the input to give the right answer.
It’s not the computers fault, it’s just a really simple decoder. If someone more Mopar savvy wrote a decoder it could work a lot better. The rules the “educated humans” are using aren’t that complicated, they’re just not programmed into the current decoders. Which haven’t changed in a decade or more.