Running einvoice-preflight over the public ZUGFeRD corpus, two EXTENDED-profile "Warenrechnung" sample invoices drew three arithmetic errors each (net total, tax total, tax breakdown), though the files are valid. The tax breakdown said the 19% basis was 321.40, 5.10 lower than the lines; our reading said 5.60.
The cause was not the allowances. The samples carry a 3.00 freight charge as SpecifiedLogisticsServiceCharge, a CII element only the EXTENDED profile uses. We read allowances and charges from SpecifiedTradeAllowanceCharge and never looked at this one, so the charge was missing: 8.10 of allowances at 19%, less 3.00 of freight, is the file's -5.10; without the freight we computed -8.10.
The checker now maps it as a document-level charge. Both samples now draw only the placeholder VAT-id warning (INV-023), the corpus's other files are unchanged, and a test pins the behaviour. Lesson: false positives on official samples are worth tracing to the element, not just tolerating.