'35 Early vs Late clarification

[Road Trip]

I have a '35 Fordor hump sedan, and I've run across a few things that tells me it's an "Early" '35. My inner fenders are not louvered; the cowl is sans X at the side of the firewall. When did the changes occur, and are some parts more / less desirable / rarer than others due to it's "earliness"?

Thanks in advance.