If I had to sum up the crucial idea of learning as a cumulative process of forgetting and remembering and in one sentence, it would be this: "the act of retrieval is itself a potent learning event." (Bjork, Bjork 1992)
Retrieval practice isn't about testing whether someone has learned something, it's actually a vital part of the learning.
In other words, learning doesn't happen in a single lesson or episode where the teacher has "covered" the content. It happens over repeated episodes where we encounter, forget, retrieve, associate and consolidate that knowledge.
This process doesn't fit neatly into the boundary of a lesson unit which is why asking teachers to 'show learning in a lesson' is so misguided. What you're seeing is merely the briefest glimmer of learning which might lead to actual learning but which depends greatly on what happens next.