23.After the suffragettes finally were told they could vote, it was overseen by the League of Women's Voters.

Rewrite:

23.After the suffragettes finally were told they could vote, the voting was overseen by the League of Women's Voters.

Why?

Here the "it" does not refer back to any previously named noun. Presumably, it is referring back to the "voting" that the suffragettes had won. Therefore, "voting" should be specifically mentioned.