Yes, most administrative programs, think hospitals, municipal, etc had a year set only in 2 digits. Yesterdays timestamp will read as 99 years in the future, since the year is 00. Imagine every todo item of the last 20 odd years suddenly being pushed onto your todo list. Timers set to take place every x time can't check when last something happend. Time critical nuclear safety mechanisms, computers getting stuck due to data overload, everything needed to be looked at to determine risk.

So you take all the dates, add size to store additional data, add 1900 to the years and you are set. In principle a very straight forward fix, but it takes time to properly implement. Because everyone was made aware of the potential issue IT professionals could more easily lobby for the time and funds to make the necessary changes before things went awry.