Question:
There is nothing wrong with quoting from the Snell Institute summary but when discussing the paper it is probably a good idea to use it. The Snell summary is not discussing the 1989 study. BTW do you know if this later study has been published in a peer reviewed journal?

Answer: Helmets decreased the risk of head injury by 69 percent, brain injury by 65 percent, and severe brain injury by 74 percent. These results, using emergency room controls, are the same as the results obtained in our 1989 study. Had it been possible to use population controls in the current study, the overall protectiveness rate of 85 percent for head injury and 88 percent for brain injury reported in our prior work would in all likelihood have been obtained.

Injuries were assessed using the Abbreviated Injury Scale (AIS) for injuries in individual body regions, and the Injury Severity Score (ISS) for overall measure of severity. A commercial computer program, TRI-CODE, was used to ensure consistent and accurate coding and injury severity scoring for data gathered from seven hospitals.

It is obvious that T&R had data about the type of injuries sustained and their severity, including both head and non-head injuries. Since they also wrote

Information was collected on possible differences between cases and controls (e.g., crash severity) that could obscure the central relationship between helmet use and head or brain injury, thus permitting needed adjustments between comparison groups through multivariate analysis. Analyses were also conducted on sub-groups (e.g., different age groups), different circumstances of the crash, and different helmet types.