Hi!

While tracking a Finnair flight from Rome to Helsinki, I noticed a discrepancy between the IATA flight number and the ICAO number.

For the flight in question, the IATA code was AY1764 while the ICAO code was FIN7NB. FIN7, on the other hand, seems to belong to completely different flight: AY7 from Miami.

Why the discrepancy?
Is there any significance in the letter suffix (NB in this case)?