When Yamadutas know that Narayana is supreme (SB 6.1.41) why do they later (6.3) ask Yamaraja if there is anyone above him?

From: SCCD

When yamadutas are talking with Vishnudutas they are telling Lord Narayana is supreme(SB 6.1.41) but later when they went to Yamaraj they are asking is there anyone above to you.

why they are asking even they know?