incident reports typically show hours that are declared by the pilot. If the FO believed the standard 200 hour pre-jet hours are not relevant to the investigation, he didn't declare them. The other FO with 412 hours thought it would be a good idea to show that he did something else before sitting in a jet, so he declared them. In either case, the investigator won't chase up their logbooks to verify the hours as in a lot of cases it makes no difference to the investigation..
regarding the 1500 hour requirement in the USA, it is stupid, it is damaging the industry and has no basis whatsoever. I'm not sure why you brought it up? I'm not aware of a single incident investigation result where a safety recommendation would have been made to increase the minimum hours for FOs, if you know any, please share