Is a superconductor really a super conductor?

Physics theory and experimental reality have something like a mathematical epsilon delta relationship, imo.

Here is a review of the matter. From the introduction in the PDF of the paper Resistance in Superconductors:

The ability of a wire to carry an electrical current with no apparent dissipation is doubtless the most dramatic property of the superconducting state. Under favorable conditions, the electrical resistance of a superconducting wire can be very low indeed. Mathematical models predict lifetimes that far exceed the age of the universe for sufficiently thick wires under appropriate conditions.

In one experiment,a superconducting ring was observed to carry a persistent current for more than ayear without measurable decay, with an upper bound for the decay rate of a part in 10^5 in the course of a year.

However, in other circumstances, as for sufficiently thin wires or films, or in the presence of penetrating strong magnetic fields, non-zero resistances are observed.

Some experimental plots are included.

Below certain critical thresholds, such as temperature, current, magnetic field and magnetic impurities, the DC resistance is exactly zero.