If I claim my son who is over 24 as a qualified dependent with OCD (obsessive compulsive disorder) on my earned income credit, what documents would I need to submit along with my return?

I have 2 letters from psychologists verifying that my son has OCD,  and social phobia. However, these are dated 4 years ago when the last time he saw psychiatrists for his condition. He hasn,t taken hardly any medications either because the costs are just too much for us to cover.
Could we possible summit these letters although they are 4 years old ?