Until now, we follow the practice of recording the date - especially, the year only by the last 2 digits (for example, 18 in place of 2018 and so on).
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.