From a lawyer friend:
*Very important message*
While writing a date in the upcoming year 2020, we should write in its full format, e.g. 31/01/2020 and not as 31/01/20., bcoz anyone can change it to 31/01/2000 or 31/01/2019 or in between any year to suit his convenience.
So be cautious about this. Don't write and also don't accept it in any documents, lest it could lose its importance.
This problem will persist only during the year 2020.