I'm unaware of precedent, but yes you did a 200 IQ connect the dots there. This seems to be really specific to the kind of mercenary work that was going on in the 20th century.
The 2000s PMC gold rush skirted around the convention by not having the contractors act as combatants. They weren't even allowed by the companies to wear camouflage in theater to signal their non-combatant status. Obviously they were also working in an environment where if they were caught by insurgents the conventions would be as useful as a chocolate teapot.
Unfortunately, that's the end issue we've spent 3 threads circling around. By the letter of the law, mercenaries have only really been notably seen back when Mitchell WerBell III and Mad Mike Hoare (May they rest in peace) had a fun time in Seychelles. Of course, here we probably 75 years later, and because the major powers have all semi-meekly sidestepped the convention to use the legally-distinct PMC moniker (Even though we all know by now that
Xe Blackwater ended up deliberately involved in some of the fighting themselves), we have basically no precedent to go off of legally since no one wanted to risk having one set by the ICC or a similar institution. Instead, all we have is being able to look at individuals and groups, see they fit the conception of the solider of fortune/adventure archetype, and then whatever you call them is almost guaranteed to be wrong because at the end of the day,
legally speaking, there's no mercenaries in Ukraine according to international law. All we have technically are the equivalent of 1930's International Brigades and super-kontraktniki because no one wants to lose their access to plausible deniability units made up of ex-vets and whatnot (Yes, even the non-ICC member US) or the ability to just use other nations' manpower to fill uniforms, and any statement to the contrary is wrong even though most people are inclined to agree to a certain point it's what they are.
I utterly despise trying to understand or explain international law elsewhere sometimes (specifically because a lot of it is either incredibly convoluted or outdated bullshit), and this convention is just one of several reasons why I don't, and also part of why I personally don't like the UN and routinely think of that one "(UN)involved in Peace" photo op when they're brought up.
Sometimes they do good stuff, other times you get this convention that's now worth less than an Iraqi dinar after 2003, the IMF's international usury, and the dozens of verified reports that crop up after every single peacekeeping mission that the blue helmets sent seemed to absolutely love having sex with children. But that's all not really relevant to this point. There's so many new ways to engage in international profiteering during armed conflict on an individual level now that the legally accepted definition means jack shit.