How can I keep track of a "role" in an organisation (eg. secretary) over time (1980-1995)
Welcome to CiviCRM StackExchange Daniel!

The CiviCRM relationships functionality will work perfectly for your use case scenario -

https://docs.civicrm.org/user/en/latest/organising-your-data/relationships

You can have different relationship types (roles) and they can be linked between individuals and organisations. A contact can also have multiple relationships.

And of course relationships include both a start and end date.