The majority, a huge majority, of fights are fought at a contractually agreed upon weight that has zero to do with the established weight classes. I know a junior welter that always fights at 145, 146. Though he can go lower, his opponents are often coming in on 2 weeks notice, for example, and they fight at a contractually agreed upon weight.
It is curious to me how this works out...A guy has been cutting to weigh 147 (160, whatever) for as long as it takes him to get on and off the scale. The he rehydrates to 165 and wins that is ok. But if somebody ropes him into having to weigh 145 (157, whatever) for that few minutes before he rehydrates to 165 and he loses...then the whole thing is horrible and unjust.