On the pump, it actually is a fuel return line, it's simply another pressurized outlet just like the main outlet but,,,,, it accesses a higher location in the pump canister. So if there is any vapor in the pump it will be purged out hence it is called a vapor return,,, however, after any vapor is purged you can be assured it will be pissing liquid fuel at the same psi as the main outlet. Of course the main outlet is sourced at the bottom of the canister for (hopefully) liquid fuel only.
Also, regarding the filters, check the Pontiac A-body's like 65-66, they had applications which used a filter with a vapor/fuel return line. So instead of being sourced at the pump, it was sourced at the filter.