The first US type Certificate for an airplane was issued in 1927. Before that US aircraft had no certification. Homebuilt and kit built aircraft were very active until the 1930's. At some point in the thirties homebuilt aircraft were in theory grounded except in Oregon where the state allowed them to fly. In reality people like Bernard Pietenpol continued to fly. There were also a few airplanes certified in Experimental sub categories with racing and research and development being two examples.
I think most people today believe EAB came about because of EAA. EAB rules were first published in Oct 1952, three months before EAA was formed.
The EAB rules came from efforts by the Oregon Group.
The EAB rules did not provide for passenger carrying. EAA discussed seeking passenger carrying approval but little was accomplished.
In Oshkosh Steve Wittman gained certification of his Wittman Tailwind in Jan 1953. In Dec 1953 Steve performed load test and dive test with the CAA observing. The Tailwind became the first EAB aircraft certified to carry a passenger. (Not for hire)
 
EAA's Sport Aviation magazine had a great article about the Wimpy last September. I must admit that, until I read that article, I did not know about Les Long or about his important contributions to homebuilt aviation. (All I knew was that Goerge Bogardus had flown his Little Gee Bee to DC three times around 1950, which was key to getting modern E-AB rules passed).

I feel somewhat embarrassed admitting this, because (A) I think of myself as someone who knows a lot about aviation history, (B) I myself am building a low-horsepower single-seater and relying on a low span loading to ensure minimal drag, just like Tom Story's approach as described in the article... and (C) I'm sitting in Beaverton, Oregon, as I type this!

In any case, check out the Sport Aviation article. It's really remarkable how much of E-AB aviation owes to these airplanes.
 
I don't remember any specific mention of it but George Bogardus must have obtained special permission to make the trip to Washington.
I have never been able to confirm it but Steve Wittman's 1938 Buttercup and 1945 Big X must have been certified in Research and Development subcategory of Experimental. He told the story of a flight with four in the Big X to the West Coast and was in Rapid City when someone at the FBO told him the CAA was looking for him. He thought he was in trouble but it turned out to be an inspector from Milwaukee who just wanted to say hello.
John Thorp did at least one trip from CA to the East Coast with his wife in the Skyscooter. All of those airplanes were crew member only.