I'm reminded of an incident I read about in Reader's Digest over 20 years ago.
Okay, I don't remember everything, but I'll set it up as best as I can.
The location was Washington DC, it was a heavily travelled road, but there was construction going on.
A number of people, confused by the construction and detour signs, turned into a restricted area.
The guards at the restricted area were issuing tickets, for trespassing. The fine was something like $200.
Here's the deal: Standard ticket thing. By paying the ticket you were pleading guilty*. HOWEVER, the code that the guards were using? It was felony trespassing. It might have been something else.
In short, many people, without representation with a lawyer, without ever being arrested, appearing in court, seeing a judge, without having their rights read to them, pled guilty to a felony by mail.
It wasn't discovered until one guy was trying for a security clearance/background check and he got asked why he hadn't disclosed that he was a feloon. Investigation occurred, and it was eventually figured out.
The good news was that, many thousands in lawyer fees later, that a judge decided that the state had failed in its duties to inform the accused of just what they were pleading guilty to, and lowered it to the equivalent of a citation, not a felony.