'Artists painting in traditional mediums generally use other scales of lightness. Many painters use the system promoted by Denman Ross (1907), consisting of nine tonal levels from black to white (inclusive). Such a scale can be created by mixing a medium grey visually halfway between white and black, a light and a dark grey halfway between medium grey and white and black respectively, and intermediate greys in the four intervals so created. Ross designated these levels by a system of letters: Blk, LD, D, HD ,M, LLt, Lt, HLt, and Wt.'
http://www.huevaluechroma.com/081.php

In the diagram that comes right after the paragraph containing the above excerpt, you will also find a VR column. Could this perhaps be the early abbreviation for very?

The link below refers to a 'floss conversion chart' used in stitching and embroidery. In it, you will find Vy Lt next to the colour samples for DMC floss products.
https://www.cyberstitchers.com/stitching_tools/floss_convers...

HTH