It is your prerogative...
I have this wonderful little book, the "Airman's Information Manual," with a list of all the standard abbreviations. It was published by an ICAO-affiliated organisation you may well have heard of, the Federal Aviation Administration of the United States of America. Therein Vz does not appear at all while Vx and Vy are not considered to designate flight along the X and Y axes respectively, hence my scepticism towards this fresh input.
I must admit to occasionally having been proved somewhat less than all-knowing (what my detractors choose to call "ignorant") about all points of flying. This has led me to creep along rather cautiously when drawing conclusions about such things as here an accident or whether some fresh input is valid or not, perhaps even what the Brits call "duff gen," hence my question to you.
This is an old copy of the AIM I am working from so that I will look to see if Vz appears in the latest edition when, if so, you may expect a prompt aplogy by PM. Until then!