Terminologies such as "full synthetic" or “synthetic blend” or “premium mineral oil” refer only to base oil, and not to additives. Group-3 oils are often called “synthetic”, not because of their origin, but because of their characteristics, which are comparable to some man-made products. These terms are not based on any particular scam by the individual oil companies. Instead, they were set up by the API (American Petroleum Institute) that everyone uses. Anyhow, one should not get overly picky and get bogged down too much about those terms. Try to understand their (oil companies) position, too. They are in a fierce competition for consumers, and one should tried to understand what would the consequences be if they would just laid out blending composition of their product, with which they intend to get the upper hand on the very competitors.
As for the additives, the only terminology that refers to “synthetic” additives is the term “ashless”, which means that the additives in certain product (most frequently referred to turbine oils and hydraulic fluids) are non-metallic based, or man-made.