ATCast. With the availability of various magic boxes permitting Joe Public to watch "radar" on his PC, several enthusiasts web sites have sprung up dealing with matching hex codes against aircraft registrations, etc. Considering the extremely high integrity of SSR I think you might be surprised at the poor integrity of Mode S information as far as hex codes go and positional inaccuracies with ADS-B are a daily occurrence. Take a look at this picture of an SBS display yesterday.
MSR777.jpg :: Other subjects :: Fotopic.Net
At the time the picture was recorded, MSR777 was actually established on the ILS about 7nm behind the one ahead. This is not a one-off, but one of anything up to a dozen in one day I have seen. Airline and type are irrelevant but whether particular aircraft always display this problem I do not know.. Safe to say that from the ATC aspect, I imagine that this would be unacceptable.
I'm very interested in this subject and would be glad to hear more..