So on the above theory, if you wanted it to be the post date all the time then you would use %%date%% unfortunately with Yoast it shows the day as well as month and year.
Or if you were developing a title to try and make search engines believe your content is current by adding the date relevance, i.e How to do this kind of thing 2017 , then you could use %%currentyear%% and %%currentmonth%% which would dynamically change based on the actual current month and year and not the post date.