LON = LGW, LHR, LTN, LCY, SOU. You can search for flights to LON, but you can only book flights to LGW, LHR, LTN, LCY or SOU. You can’t book a flight to LON.

You baggage tag won’t show LON, it will show the airport

IATA hasn’t assigned a code, yet, for the new airport because it is not yet possible to book a flight there. Once you can IATA will assign a code, and it won’t be BER.

ONT = Ontario, CA, BUR = Burbank, LGB = Long Beach, none of which are in Los Angeles.