Sometimes these groups don’t even need official names. At least, they didn’t in the past as there is a long stretch going back to the dawn of time. Nature encourages mercenary groups to form and evolve into the modernized culture. Humans are constantly at odds and sometimes need that 3rd party to intervene. Third parties have largely been very effective in settling violent disputes.
There are many tasks that a mercenary group takes on. Over time, some tasks are more important than others -depending on the threats and stage of the conflict. The mercenaries can be used before, during and aftermath of a conflict. Each stage of a conflict puts a mercenary into different responsibilities.
Blackwater served their purpose for a particular period of time and then morphed into another company with slightly different responsibilities. They still perform the basic securities though and still carry the necessary weapons in performance of their duties.
Mercenaries come from all over the world. So, with each different mercenary group, such as one from Argenia, they carry with them different cultures and perspectives on mercenary objectives. I watched a video where some Indians worked in Iraq to protect an embassy. The mercenaries don’t drive in protected vehicles to get to and from work. Part of the reason the Indians don’t need extra protection in Iraq is because they are not white. All white skinned people get targeted because they stand out from the locals. Indians do not. White people in dark countries need far more protection.
Hiring particular mercenaries with certain races has been very effective for the trade. For example, hiring Mexicans to protect the Mexican border is more effective than hiring white people. The Mexican border control is more naturally suited to work in the hot harsh conditions. Not only that, they can understand the illegal border crossers much better because they tend to speak the same language and look like their brothers and sisters. There is a familiarity that makes them more comfortable with each other.
Mercenaries spring up in groups, and sometimes the best ones come from an already war-torn country. Those kinds of mercenaries have the experience and may have trouble getting jobs anywhere else. Since they come from the same place as a group, they can form more tightly knit bonds and coordinate their actions amongst each other more effectively. There are no individuals in a mercenary group that act effectively alone.
As certain private military groups recieve bad press, other different named groups take their place.