Puerto Rico's Treasury Department has published Administrative Determination (AD) No. 21-08 of 20 September 2021, which amends AD No. 21-05 of 11 May 2021 in regard to the general 51% disallowance of deductions for cross-border expenses incurred with related persons not engaged in trade or business in Puerto Rico. AD No. 21-05 provided that the relief from the 51% disallowance is provided when…