5e does not have different skill levels. "Expertise" is not a skill level in 5e. It is the name of rogue ability that allows them to add double proficiency bonus to certain skills. They have it because they are a Rogue, not because they are better at a skill.To me, that explains the steps between non-proficient to proficient and proficient to expertise, but not the jump from non-proficient to expertise.
The other thing that happens frequently is the retcon. In Doctor Who: The Pyramids of Mars Sarah Jane Smith is suddenly an expert marksman, even though she had never shot anything at all in any earlier episodes. Who is to say that a character hasn't had that skill all along, but just has never used it before?