Vref is not ‘referenced’ to something; it is a reference speed for landing performance and is published by manufactures as a reference for the pilot to use during the approach.
CS/JAR/FAR 25.125
VREF may not be less than –
(i) 1.23 VSR0;
(ii) VMCL established under CS25.149(f); and
(iii) A speed that provides the manoeuvring caability specified in CS25.143(g).
CS-25 ammendment 1. via
EASA