Well....Luke was the last jedi and quit making Rey the last Jedi in the end. So, hopefully the loophole here is that baby yoda doesn't become a jedi so he's still around but maybe he equivalent of an 7 year old come ST time.
As far as anybody in the resistance new, Luke was the last of the Jedi. As he was focusing on training his new students, he was probably giving that his attention To that and not searching the force for those on the outskirts. After he decided to quit, he cut himself off completely from the force and even Yoda could not contact him. So they were probably out there, he was just unaware of them, and nobody else even thought that there might be others besides Luke.