The mirroring of the numbers (first and second half in a year) occurs only once a century – so the year 2020 is significant for many reasons. It is recommended that when you’re writing down dates in official and legal documents, write the year in its full four-digit form (2020).
It is best to avoid abbreviations such as the two-digit form “dd/mm/20”, as irresponsible parties could change the number for their own motives, with negative implications.
Recent recommendations also warn the public not to accept official documents with dates written without the full form, to avoid any future problems.
When we write dates such as 31.1.19 it does not mean nor is it taken to be the year 1819 or 1919, but 2019. When writing 31.1.20, there is potential for ambiguity and the ’20’ can be altered to anything from 2001 to 2019.
It is always good to be clear and specific, so write in full.
We certainly won’t be around for the next time, in 3030.