No they haven't. No one has gotten pairs to "coexist extremely well". Some people some of the time keep them in pairs, and they didn't get sick or die during that time. Doesn't mean it was a good situation.Yes they have. In rare instances. With proper care, constant vigilance, and luck. But it’s something I would never recommend to a new tortoise owner especially with testudos. Even redfoot pairs that are generally peaceful are a bad idea. The male likely won’t directly hurt the female (usually) but will harass her to death. But to definitively say it’s impossible is not accurate. I have a Greek pair together now for the last 3 years. Zero issues. I kept a sulcata pair together and they always ignored each other. I gave them to a friend when they got to about 20” because of space issues and they’re now part of a larger group but in the years I had them they did great. Tortoises aren’t machines and if we study them close enough we find that all of them have different dispositions and personalities. Matching those dispositions to their general needs is key to proper keeping. The goal should be a group with proper sex ratios depending on species or separate enclosures. Even then it’s not an exact science. How many of us have had the “perfect” ratio only to find one female in that group was the harasser? That’s certainly not the norm but it happens. Point is, there are tons of ways of doing this and not all of them are wrong or just opinions. I think it’s great folks come here to seek advice. Seeking a variety of opinions and doing thorough research makes the world go round.
Because you fail to recognize the signs, and because your pair survived, does not make this a good practice. One of them will be dominant and the other submissive. This is true of all life forms, and as Will once pointed out, this is even true of flatworms. Pair dynamics are full of problems. Because two tortoises living together are still alive does not mean these problems weren't there. I agree that all torts have differing personalities. Some are more tolerant that others, but this does not make it okay to keep them in pairs, or tell other people that you think its sometimes okay to keep them in pairs. It isn't.