Read it again. It says
Moreover, the warranty extension will apply retroactively to all Model S vehicles ever produced. In hindsight, this should have been our policy from the beginning of the Model S program
You should read a copy of your ACTUAL battery warranty document. Here is what mine said for my 2013 P85 (which I bought in 2016, after the blog post you mention) So the post never extended the warranty of those original S60s.