Did Palpatine really think Luke could become a Jedi?

Question

In episode 5, The Empire Strikes Back, Emperor Palpatine seems worried that Luke could become a Jedi.

VADER: What is thy bidding, my master?

EMPEROR: There is a great disturbance in the Force.

VADER: I have felt it.

EMPEROR: We have a new enemy - Luke Skywalker.

VADER: Yes, my master.

EMPEROR: He could destroy us.

VADER: He’s just a boy. Obi-Wan can no longer help him.

EMPEROR: The Force is strong with him. The son of Skywalker must not become a Jedi.

VADER: If he could be turned, he would become a powerful ally.

EMPEROR: Yes. Yes. He would be a great asset. Can it be done?

VADER: He will join us or die, my master.

By this time, both Sith Lords believe all the Jedi are dead. Even Grand Moff Tarkin believed that Vader is the last of their kind, and that was back in Episode 4.

VADER: He is here.

TARKIN: Obi-Wan Kenobi? What makes you think so?

VADER: A tremor in the Force. The last time I felt it was in the presence of my old master.

TARKIN: Surely he must be dead by now.

VADER: Don't underestimate the Force.

TARKIN: The Jedi are extinct. Their fire has gone out of the universe. You, my friend, are all that's left of their religion.

Did Palpatine seriously believe Luke could become a Jedi?

Unless Palpatine believed some Jedi remained in hiding, he should have assumed that nobody could have trained Luke. It took years of training to become a Jedi, so he should have assumed that even though Luke was very sensitive to the Force, nobody could train him to hone his innate abilities into real skills.

Please provide answers with quotes from canon sources. Is there a canon source that says Palpatine believed some Jedi were still alive and capable of training Luke?

Answer 1

  In-universe explanation would be that Palpatine didn't know what happened to Yoda. According to the novelization of "Return of the Jedi", he only learned that Yoda died when he finally met Luke in person. Also, in the new canon there are other interesting possibilities, like Ezra or Ahsoka Tano training Luke. Finally, a whole can of worms is opened with "World between Worlds" and time travel, with someone from the past possibly being able to contact and train Luke. It is worth of mentioning that Palpatine and Vader probably didn't know that Kenobi barely trained Luke, instead of using the usual Jedi method - training from birth.

  Out of universe, when "Empire Strikes Back" was created it was still unclear how Jedi are really trained, did they start as kids or as adolescents like Luke, did they need teacher the whole time or could they learn things on their own. It was even unclear if Palpatine knew about Force Ghosts.