Why we should use date format as 'dd-mon-rr'? Why not 'dd-mon-yy'?

Question

Specifically why "rr" must be used instead of "yy" in date format. What is the use of "rr" format?

Answer 1

both formats are similar, but the RR format provides additional flexibility for storing date values in other centuries. The RR datetime format element lets you store 20th century dates in the 21st century by specifying only the last two digits of the year