The Y2K Bug goes into the issue of some programs seeing "00" as 1900 rather then 2000. A resulted issue is that 99 and 00 were used as special codes in “year” data fields.
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In retrospect the Y2K Bug was more sound and fury then an actual threat. Unix has been able to handle dates all the way to 2038 since 1970, the 1984 Mac OS could handle a few years past 2000 before having issues (and that issue disappeared when the OS when full 32-bit in 1991) and Windows had gotten to the stage where it could handle more then two numbers for the year before the 1980s were out.