Zach- All 8 of the original American League teams were formed on their own and not teams migrating from the National League or the American Association where many of the owners were rounded up.
I don't know where you found the starting dates but all eight of the 2012 Media Guides for the original 8 AL teams simply list their origins back to 1901 and Ban Johnson's new league.
Until recently the Yankees have even been reluctant to add the 1901 season in their history though it was certainly their start in Baltimore!
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