Deterministic FIFO/LIFO & 8-Digit HTS Substitution Matching Under 19 U.S.C. § 1313(b)/(j) TFTEA Modernized Customs Drawback and ACE CATAIR Per-Unit Averaging Limits

Section 906 of the Trade Facilitation and Trade Enforcement Act of 2015 (TFTEA, Pub. L. 114-125), codified at 19 U.S.C. § 1313 and implemented by U.S. Customs and Border Protection (CBP) under 19 CFR Part 190, replaced subjective commercial-interchangeability and same-kind-and-quality drawback standards with objective 8-digit Harmonized Tariff Schedule of the United States (HTSUS) subheading substitution, coupled with mandatory electronic line-item per-unit averaging (PUA), strict lesser-of-duty-or-value substitution caps under 19 U.S.C. § 1313(l), and a five-year statutory importation-to-filing horizon under 19 U.S.C. § 1313(r)(1). Despite objective tariff matching, enterprise drawback claims routinely fail CBP Automated Commercial Environment (ACE) Customs and Trade Automated Interface Requirements (CATAIR) validation (error classes F540–F543) or incur post-summary audit clawbacks due to four algorithmic defects: premature IEEE-754 floating-point rounding of per-unit duty averages across split designations, failure to escalate 8-digit 'Other' basket provisions to 10-digit statistical suffixes, misapplication of 19 CFR § 190.14 fungible inventory accounting rules (FIFO vs. Low-to-High domestic lot depletion), and contamination of refundable Section 301 pools with statutorily barred Section 232 national-security tariffs. This technical note formalizes an exact rational and scaled-integer bipartite matching methodology with SMT-verified tariff-hierarchy gates and residual-conserving CATAIR ledger invariants. Reference Verification Implementation: https://drawbacksovereign.com (Maintained by TITAN Capital Forensics LLC, Albuquerque, New Mexico, USA; D-U-N-S: 33-195-8002; UNGM: #1299169). Zero source code or executable software distributed.