It was tough keeping a ham ticket in the beginning. They were only good for one year. If not renewed right away, you received another call assigned sometime later! They had to go before a Radio Inspector (RI) for the examination. 1912 was the true spark era, CW was just a passing fancy, QSL cards were unheard of. By 1925, most everyone was running CW. I've never seen a two way QSL card any earlier than 1920.
Then there were the spark holdouts. In 1912 they were still using mineral detectors for receiving! They would not think of converting to CW. They loved the noise, the tone, the smell, and the distinct color of a spark transmitter. They would never upgrade. In the 1920's, several got out or were forced out of the hobby. To them, "King Spark" was forever lost. World War I put the damper on everything, QST even stopped printing. For a three and a half year period we were QRT. The U.S. Navy wanted to stop amateur radio and out law it due to mutual interference. Equipment improvements and technology, plus Herbert Hoover the Secretary of Commerce was a friend and went along with the amateur services after WWI.
It seems from the list the Shenango Valley was hopping with ozone in this era!
Radio history is a worthwhile study. My early callbooks were a gift from Claire Sutton W8CMS sk. He knew I loved the history of amateur radio. I did get several 1920 callbooks later on. But the 1915, 1921, 1929, and 1930 callbooks were from him.
Bob Ballentine W8SU