Each successive lesson heading gives some words which are to be introduced in that lesson. However, the forms shown in the heading are often not covered in the lesson. Why?
This is because the words are added as entire sets of forms, which means they technically also include forms which are taught later. In practice, some forms do not appear immediately, even though they are classified as belonging to an earlier skill – they are introduced in skills that feature the respective case. So “twojemu” (Dative form of “twój”) will appear in the skill where the Dative case is introduced.
So you shouldn't worry, it is done this way to optimize the learning process. We would rather not see the more “advanced” forms displayed in early skills, but this is how Duo works, there is nothing we can do about it.