Which of the following add types means the system assumes the last entered value is valid if not populated?

The correct answer is Lookback. This add type allows the system to assume that the last entered value is valid in scenarios where a new value is not provided. Essentially, during data entry or processing, if a new input is absent, Lookback automatically retrieves and uses the most recent valid value from prior entries. This is particularly advantageous in environments where continuity and efficiency are necessary, as it reduces the need for repeated input of the same information, ultimately streamlining data management and minimizing errors.

In contrast, other add types do not function in this manner. No-Add would imply that the system does not accept new entries in certain cases, while Response each time would require a fresh input for each instance, disregarding the previous data. Instant typically involves immediate processing of data entries without validating or referencing past inputs. Thus, Lookback is unique in its ability to enhance workflow by reusing the last known valid entry when new information is not provided.