The report does indeed give details of the safety data from 1981 to a date before the recent spate of accidents.
UK Oil and Gas have been keen to publicise the 'improving helicopter accident rate', until the data showed that was not the case. As with all statistics the detail is the critical aspect. Choose your data set and many things can be proven. Data back to 1977 has frequently been used to demonstrate the trend mentioned above.
A couple of points worth noting. All North Sea data would not unnaturally include the UK. Thus any differences would be partially masked by that inclusion - any differences would be partially from the UK plus the rest rather than directly against the 'rest'. So the data being presented is not a true comparison. For that you need the direct Norway - UK comparison.
Even here you need care as the EC225 shaft failure might have occurred in Norway or the UK as it is notionally a parts related failure - although again there were a lot of human factor elements in failure to deal with the defect.
But if the accident rate from one side of the North Sea to the other is so different luck or mis-fortune over more than 15 years seems a poor explanation.