Plugin uninstall only removes one table
Thanks for that tip, Lindsey, but here's what happened: I changed calendar37 to calendar37_Occurrences and then all three tables wouldn't uninstall.  It turns out that the issue is having a capital letter after the underscore.  So it seems like an "undocumented feature" that you can make plugin tables persist after uninstall by including a capital letter after the underscore.

return 'calendar37_Subsets';
return 'calendar37_Views';


needed to become:

return 'calendar37_subsets';
return 'calendar37_views';