We use the strategy of versioned events. Event data is still immutable, but older events are upgraded to the latest structure at read time. This works reasonabl

We use the strategy of versioned events. Event data is still immutable, but older events are upgraded to the latest structure at read time. This works reasonably well but it is not ideal. Storing data as immutable events implies that all data ever generated by your application becomes available to future versions of your application. Writing an application that can handle all the forms of your data across time is obviously more complex but it's a necessary consideration if you decide to go with event sourcing. Unfortunately, you cannot have all the benefits of available and useful unaltered historical data without also putting in the engineering effort to support it.