Non-Dynamic Evidence does not have the concept of Evidence Type Versioning present in Dynamic Evidence. With Non-Dynamic Evidence, every piece of Case Evidence recorded over time has the same data structure and the same user interface. This can cause problems if, for instance, legislation changes to require an additional piece of Evidence Data to be recorded. An entirely new Evidence Type would need to be created, and code and user interface modified to take this into account; alternatively, the existing Evidence Type would need to be modified and either data migration would be required to populate the new field for existing Case Evidence records, or code would need to take into account the fact that the attribute would not be present for some Case Evidence records. Either way, it is awkward.
Dynamic Evidence, however, includes the concept of Dynamic Evidence Type Versions, allowing the structure of Case Evidence to change over time. A Dynamic Evidence Type might have only one Dynamic Evidence Type Version or it might have several, forming a timeline of modifications to the structure of the Dynamic Evidence Type.
The date on which this hinges is the Effective Date field of the Dynamic Evidence Type Version. The timeline begins with the Dynamic Evidence Type Version with the earliest Effective Date and extends to infinity in the future (there is no end date). The period of time during which each Dynamic Evidence Type Version is active extends to the day before the effective date of the next Dynamic Evidence Type Version in the timeline.
There are restrictions on what you can and cannot do when administering Dynamic Evidence Type Versions. One restriction is that you can only change the effective date on a Dynamic Evidence Type Version when it is in an 'InEdit' status, not when it is 'Active'.
You cannot create a Dynamic Evidence Type Version with an Effective Date earlier than an existing Dynamic Evidence Type Version, because this could render processing of existing Case Evidence records ambiguous or incorrect. Likewise, if you are creating a new Dynamic Evidence Type Version to supersede an existing one, there should be no Case Evidence records for the Evidence Type for the period that the new Dynamic Evidence Type Version would cover.
Note that there is currently no administrative way to correct a live Dynamic Evidence Type Version that has existing Case Evidence records, and so it is important to ensure that Dynamic Evidence Type Versions are fully tested before live Case Evidence records are entered in respect of them on a production system.