Abbreviating the year 2020 as “20” can provide an opportunity for others to manipulate documents by adding additional digits to change the date. For instance, “1/1/20” can easily be changed to “1/1/2019” or “1/1/2021.”
Writing out the full date could protect you from issues arising where the date may be important such as checks or other legal documents. One example would be if you issued a signed check dated “1/15/20,” a scammer could change the date to a future date allowing them to cash an old or stale check. Another example would be if you enter into an interest bearing promissory note with payments starting July 1, 2020. If you write in the date as “7/1/20,” an unscrupulous party could modify the date to “7/1/2018” and you could find yourself owing additional interest or in breach of the terms of the note.
Remembering to use the full year (2020) on any legal document or check will help protect you from any fraudulent activity.