How to identify a single-wire or multi-wire core by marking?
VVG - cable with rigid single-wire veins.
PVA - wire with multi-wire (flexible) cores.
ШВВП - cord with flexible stranded cores.
PV-1 - wire with one single-wire (rigid) core.
PV-3 - wire with one multiwire (Soft) core.
Personally, I do not see any dependence, some kind of "magic" letter that talks about the structure, obviously. However, there is a standard on which letters to use for marking. If you look at the transcripts of all these products, you will notice that P is a wire, W is a cord, and H is a vinyl shell. The figure in the marking of the PV indicates a class of flexibility.
By the way, these are the main markings that you should remember (the most popular). You can read more about cable products with different markings and designs in the articles from this section of our website - https://our.electricianexp.com/en/elektroprovodka/provoda-i-kabeli