How to calculate interest in very, very long-running dispute

After 15-plus years of litigation, the remaining issues in Art Midwest Inc. v. Clapper related to the calculation of prejudgment interest.  No. 14-10973 (Nov. 9, 2015, last before the Fifth Circuit in Art Midwest Inc. v. Atl. Ltd. P’ship XII, 742 F.3d 206 (5th Cir. 2014)).  The Court reversed as to the starting date for calculating interest — even though the first judgment by the district court was reversed in part, the date of that judgment was still the proper starting point under Fed. R. App. P. 37(a) and Masinter v. Tenneco Oil Co., 929 F.2d 191 (5th Cir. 1991), aff’d in relevant part, 938 F.2d 536 (5th Cir. 1991).  The opinion also touches on waiver and law-of-the-case issues addressed in the 2014 appeal.