In the mid 2000s I lived in San Diego and played tennis at the Morley Field Complex in Balboa Park. It was a cool place because there were so many characters.
One day as I was hitting on a ball machine, a guy came up and asked if I wanted to hit with him instead. I usually say no in those situations because if I am on the ball machine I am there for a reason to work on something specific. But this guy persisted and said that he's a 5.5 player, with the clear impression that he was doing me a favor by asking me to hit. I was probably a high 4.0/low 4.5 at the time, so for a 5.5 to want to hit with me I thought was an opportunity I shouldn't let pass.
We start hitting and I immediately realize this guy has never had any formal instruction. He had horrible grips and technique, and was basically a pusher/hacker. But he moved well and didn't miss much. He suggested we play a set. I wasn't too excited about playing a pusher (it's just not fun... I know we all need to learn how to beat them, but doesn't mean I look forward to it), but I thought, whatever let's do it.
Usually pushers give me trouble, but because I had just been grinding on the ball machine my footwork and timing were on point. I slaughtered him 6-1 in like 20 mins. There was no way this guy was 5.5.
When we sat down after the set, he was clearly flustered and embarrassed. He asked if I played D1 tennis, etc., and I was like, bro, I'm barely a 4.5 on a good day. He said no way, you just kicked my ass and I win 5.5 tournaments regularly. Given my knowledge of the characters that played at Morley Field, I figured it was just par for the course. However, when I got home I looked up his record on the USTA website. He had indeed won 5.5 tournaments in the area. My brain exploded. There was no way that was possible. 5.5 is basically the open level and I had friends that were actually that good so I knew how they played. This guy would barely win a point off of them.
So I did some more research. I discovered that the tournaments in San Diego were regularly held with many levels, from 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, Open. I went back to the USTA website to do a comprehensive search for all his results. While he had won some 5.5 tournaments, he had also been double bageled in the first round of some of them. I asked some other guys at the complex about it. Apparently, because there was such a broad range, most people played in 3.5 through 4.5, and the best players played Open, leaving very few people to sign up for the 5.5 bracket. This guy self rated it seems, and signed up for 5.5. Some other similarly talented players regularly did the same, and he ended up winning some of the tournaments. When real 5.5s signed up, he got smoked.
So there was basically a group of observably low-level players playing each other in the 5.5 bracket and calling themselves 5.5's.