I agree with the previous points of view. If the land is different (uses, changes in the market, age of existing appraisal, improvements to or lack thereof, change in potential income....) you would want a new appraisal. My earlier comment about not getting a new appraisal revolved around if you have already have a newer appraisal and you are changing 2000 acres of IDENTICAL land in an area that is well know to the lending staff and you can provide stats of current sales and/or auction prices in the surrounding area to sufficiently document the file.
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Just working here until I get my letter from Hogwarts.