The reason for the problems is _not_ because all the digits are the same, but because,
 in base 10, i.e. denary, 9.9.99 comes just before 0.0.(1)00. That is, the clock has
 ticked on from 99 to 100. Therefore the problem would only arise with 9.9.99 going to
 0.0.00, because after 7.7.77 is just 8.7.77, and after 8.8.88 is just 9.8.88.
This problem, with 9.9.99, will however, only arise, if the year (99) in this case,
 is only stored as a maximum of two digits, because then when it clicks on to 100, the
 computer will interpret 100 as just 00, because it has only been programmed to hold
 the year as two digits. This programming would have been done thus, originally, to save
 on computer space (memory), which in the old days could have been very tight.
This is the root of _all_ Y2K bug problems - that the year, 99, will click on to 00, rather
 than the full 100, because somebody, a long time ago, programmed the computer not to
 bother with the 3rd digit of the year column to save on memory space.
However, implicit in your question, is a valid point, which could have been the reason for
 your confusion: calendars are not inherently denary (i.e. base 10) anyway - indeed there
 are obviously 12 months in the year, and at least 28 days in each month. Therefore any
 computer systems would have had to have coped with up to 28 days pcm and 12 months
 per annum from the offset. And so, there is nothing special about 9.9.99 either, and
 even this date would just have clicked on to 10.9.99! For this reason I should be very
 surprised if there were ANY problems at all reported for 9.9.99.
Personally I think the Y2K bug problem itself will be a complete damp squib (remember you
 heard it here first) as it would have been a very perverse computer programmer, who,
 knowing he was only assigning a maximum of two digits to the year column, put any
 safety-critical code reliant on just those two digits. (Equivalently, if you think about
 it, why should any nation's nuclear weapons, for example, be more likely to fire if the
 governing computer suddenly _does_ think it's 1900 rather than 2000. There may be many
 criteria for release of nuclear weaponry, but I shouldn't think date alone were one of them!)