They marked time from significant events. For example, 'the fifth year of the Emperor Claudius'. In ancient cultures where astronomical observations were important, these were referred to eg in Ancient Egypt the cycle of the Star Sirius was referred to when ordering events. We don't know how time was marked in cultures that have left no written record, but we can make an intelligent guess that stone circles and henge monuments were used to mark time.
200 years is a long time to retain collective cultural memories with accuracy, so it is likely that an element of mythology or story-telling would creep in. Even the highly literate ancient Romans counted the start of their 500 year-old origins in the Romulus and Remus story. So it is quite feasible that a culture 2000 years ago would account for an event 200 years previously as 'in the time when the great goddess gave birth to the land' etc.