Differentiating the "Black Robes"
For folks who didn't catch it on their own playthrough or (or watch-through) of FF7 Rebirth, here's a quick breakdown of the apparent nature of the people in black robes seen throughout both this game, and previously in Remake.
This differs from OG canon, where everyone in a black robe was a Sephiroth Copy, but in the FF7R timeline they appear to be broken into three "types."
SPOILERS BELOW — READ AT YOUR OWN RISK
NO NUMBER TATTOO means this is a G-type SOLDIER suffering from degradation. These people are terminally ill. Degradation sets in within five years of enhancement [see Note 1 below], and accelerates very quickly without aggressive treatment.
Known G-type SOLDIERs: Roche, Azul, Rosso, and Shelke Rui.
Population: over 100.
A ONE- OR TWO-DIGIT NUMBER TATTOO indicates S-type SOLDIERs in the throes of Reunion. These people are not terminally ill, based on dev comments confirming that S-type SOLDIERs don't degrade, but they have a cellular leash that is being constantly yanked on by Sephiroth/Jenova. Without Reunion taking place, most of them would presumably live long, fairly healthy lives. [See Note 2 below.]
Known S-type SOLDIERs: Zack Fair, Kunsel, Luxiere, and Broden.
Population: presumed fewer than 100.
A TATTOO STARTING WITH "SC" confirms these people are successful Sephiroth Copies. Failures do not receive a tattoo. They may or may not be terminally ill, contingent upon which type of SOLDIER they were prior to the procedure to make them into a Copy, and the leash on their own cellular makeup is much stricter, much more direct, and gives them a clearer concept of where to go and what to do.
Known Sephiroth Copies: Roche (successful), Zack Fair (declared failure), and Cloud Strife (declared failure).
Population: 4 subjects in total, plus 2 known failures.
Tattoos don't seem to be applied at the time of enhancement, since none of the SOLDIERs in Crisis Core have them, but it's possible that early inductees like Broden were marked when they survived the treatments; this seems likely, as Broden's tattoo is in a slightly different typeface than the tattoos of others in his "type."
I didn't include Sephiroth, Genesis or Angeal under known members of their given types, as they were never normal humans and were not enhanced using one method or the other as teens or young adults. Those who are Jenova babies from birth don't count. I also didn't include two members of DeepGround due to the fact that they canonically cannot actually be G-type SOLDIERs based on the lore of how the two of them were made and how they function in general; they may be G-type on paper, but they are not G-type for the purposes of this analysis.
Lastly, I'll admit that this breakdown may appear to be slightly inconsistent during gameplay, but this seems to be due only to the reuse of models between black robed individuals, presumably to take stress off the dev team. I'm fine with this, obviously, no crunch is good crunch. As far as I can tell it's pretty consistent in full cutscenes, though, so I'm sticking with it until the third game proves me wrong.
NOTE 1: The timeframe for degradation is based on Roche suffering from the condition prior to his becoming a Sephiroth Copy, which is visible in the fact that he has a handful of incongruously pale streaks through his hair prior to the procedure; an attempt to cure this is presumably the reason he volunteered to work with Hojo in the first place.
According to the Remake Ultimania, Roche joined SOLDIER after the Nibelheim Incident, so he's only been in the program for five years at the most; this timeframe also allows us to recognize S-type SOLDIERs, as they've been in the program for significantly longer with no known ill effects (e.g.: Kunsel has been in the program since at least 2000, but is mentioned by name and indicated to be at headquarters in Remake, showing that he's still on active duty in 0007; this wouldn't be the case if he were suffering from degradation, so he can't be a G-type.)
NOTE 2: The capacity of S-type SOLDIERs to live fairly normal lives with minimal major health issues is proven by the existence of Broden, who identifies himself as a SOLDIER but was certainly part of Project 0; he and Mildred left home as teenagers and wound up with Shinra, but Mildred doesn't know the name of the project into which he was conscripted, only that it was "top secret."
Combined with the apparent age of both characters in-game, this indicates that Broden took part in the project before SOLDIER was even SOLDIER, putting him as one of its earliest successful operatives, probably enhanced sometime between 1983 and 1985 based on the timeline provided in the First SOLDIER Battle Royale opening cutscene—hence why his number is the lowest shown on a person in a black robe in the entire game. This puts him in his forties at the youngest during the Crisis, and he functions just fine (albeit with some other issues we can assume were caused by the enhancement procedure being imperfect at the time of his enlistment) until Reunion starts to call him toward the end of 0007.
