Where does the brooch that Luna gives Usagi come from if she wasn't originally a Sailor Scout?


Using this as a reference [tumblr
page](https://silvermoon424.tumblr.com/post/97346293538/sailor-venus-the-
leader) where I read from the images of the manga, that Sailor Moon never
existed until the reincarnation of Princess Serenity as Usagi. Luna turned her
into a Sailor Scout to protect her real identity as Princess from the enemies.

So, then where did the brooch come from? Is this specified in any of the manga
books?

