Difference between effective dated appraisal and retrospective appraisal?

The effective date is the actual date that the appraiser is on the property, the market value at that specific time. A retrospective appraisal is an appraisal that gives the market value at another specific time other than when the appraisal is done. The retrospective appraisal utilizes information only up to the retrospective date. A good example for the need of a retrospective appraisal is fire, or the belief that a home was over appraised at an earlier date.