Thankfully, no! The extra overloads are just a performance optimization; they do not affect the returned result.
If the deployment target is lower than the availability of the CustomStringConvertible conformance, then the compiler will (silently!) select the unconstrained overload, ignoring the (partially available) constrained ones. This will result in an opaque call into the stdlib that ends up doing a runtime as? check to find description. If the code happens to be running on a stdlib version that includes this proposed conformance, then this check will succeed and we get the nice description. If we are running on an older stdlib, the check will fail and we'll get the original descriptions.
If the minimum deployment target is higher than whatever stdlib release includes these changes, then the compiler will select the constrained overloads, which results in improved performance without affecting the returned result.