Does a boarding pass scanner located at the entrance to a jetway collect information about the flight number and routing of the flight on the boarding pass? If so, is the scanner programmed for the specific flight that is departing from that gate?

I ask these two questions because there have been a number of recent cases where passengers were allowed to board the wrong plane. I don't understand how that can occur if the boarding pass contains specific flight information and the scanner is programmed for the flight departing from that gate.

How can the scanner accept a boarding pass for any flight other than the flight that is departing from that gate? The most recent case, as we have read, is the one where a French-speaking woman with a ticket from EWR to CDG was allowed to board a flight from EWR to SFO.

If the scanner does not read flight # and routing information, then what is the purpose of the scanner? If it does, how can someone get through with the wrong ticket?