Damien

Y2K was a known problem with a known solution. It isn't a hoax or a myth, it was a programming issue people understand. No one can tell you precisely why some systems were less vulnerable than others without understanding how that system handled dates and the consequences to those systems of the dates being wrong. However anyone who maintained such systems at the turn of the century would have had first-hand knowledge of what they needed to do and what the consequences would have been had they not. There are literally people out there who directly would have seen these things.

The article linked above points out some of the possible problems. The Italy/Russia/South Korean thing is a red-herring since we don't really have an idea of how much software they had to maintain at a state-level rather than using private companies which fixed the issue or working from software written in countries which deployed patches to systems running in those countries.