The short answer is that the change of millennium won't cause any problems for Ability.
There are, however, two issues of which you should be aware:
Date format - in a spreadsheet showing both 20th and 21st Century dates, you should format all dates to display four-digit years to avoid confusion (see Formattting a date for more details).
Date entry - you can enter dates using either two-digit years or four-digit years. Obviously with four-digit years, there's no ambiguity in century. Most people will be used to entering two-digit years, in which case Ability will assume you mean the 20th Century for all years later than and including 1972 and up to 1999, and the 21st Century for all other years entered as two digit. For example:
Enter date as… |
Ability understands you to mean… |
1/1/99 |
1/1/1999 |
1/1/00 |
1/1/2000 |
1/1/71 |
1/1/2071 |
1/1/72 |
1/1/1972 |