SAS internally stores the dates in numeric formats; where 1JAN1960 refers to 0 in SAS and adds 1 for each day then after.
So dates before 1JAN1960 are saved as negative numbers internally.
To cope up with dates in operational systems where YEAR figures are stored in 2 digit formats; SAS has provided a YEARCUTOFF option its value by default is year 1920.
When one provides a date with two digit year value SAS uses YEARCUTOFF option with 100 years span value.
For example: If YEARCUTOFF option has value of 1920 then SAS will consider the date span of 100 years starting from 1920 upto 2019; so the date 20JAN88 will be recognized as '20JAN1988' and date 20JAN11 will be recognized as '20JAN2011'
Though SAS stores dates in numeric format it can read or output dates in number of formats like some of the followings;
date9. - DDMONYYYY
date7. - DDMONYY
ddMMYY8. - DD/MM/YY
ddMMYY10. - DD/MM/YYYY