Are milestone charts correct?

I was reviewing the milestones chart in my new pediatricians office and realized my 13 month old son is doing some of the “emerging skills” of 17-18 month olds. For instance, he responds to directions like sit down or bring me a book. He turns the pages of a book, stacks 3-4 blocks, feeds dolls and brushes his teeth (after I do of course). Is this really advanced? Or do they not give toddlers enough credit on these charts!