Originally Posted by
Cathay Boy
Correct, authorities will review them and will discourage numbers that are similar, like (hypothetically) CX899 with CI899, usually they will do their best to ensure enough diversities. Thought a major airport like JFK I would imagine it will be very hard.
The numbers may be similar at high volume airports but I don't believe the iata codes and the numbers are similar both together at any given airport route. Plus they should be using NATO alphabet. Charlie x ray 899 vs Charlie India 899.