There is, I think, a difference between leatherette and vinyl - but it's one of era, rather than definition and composition.
To me, the sort of thin, hard, totally unstretchable seat covering that was in the 1955 Bond I bought in 1970 was leatherette. The sort of material used in my first "proper" car (a '62 Vauxhall VX 4/90) looked actually less like leather (mind you, it was metallic blue!) but was thicker and more giving, being slightly elastic. That was vinyl.
Or is that just me?