The raw denim after the sanforization process put those jeans in store before significant shrinkage. The upside is you get to the raw denim straight from the loom, but buyers beware when choosing the size to fit them after first wash.
Denim makers, typically when processing sanforized denim, set it through steam and stretch it out. That way shrinkage is mitigated by lots, before the fabric go into the sewing machine. Venturing to a rawer process, recently popularized by denim aficionados, the so called unsanforized denim is taken from the loom straight to the sewing machine. Thus the term, “live in,” “break-in” or “shrink to fit,” as the fabric gradually molds to fit the shape of the owner.
Typically, unsanforized denim will shrink about 10% over time. The perfect fit could be achieved if you can wear your preshrunk jeans in the bath tub for half an hour. Set the water to around 30 to 40 degree Celsius. Or if you cannot endure the grueling process of affection, simply soak your new pair in that warm water for the same duration. Hang it dry in the open, by the belt loops. This is to ensure its new shape it has gotten into.