This is from paragraph 299 of the Tuna report, where the Appellate Body sets out its conclusion on TBT 2.1:
We find, instead, that the US "dolphin-safe" labelling provisions provide "less favourable treatment" to Mexican tuna products than that accorded to tuna products of the United States and tuna products originating in other countries and are therefore inconsistent with Article 2.1 of the TBT Agreement.
The reference to "tuna products originating in other countries" makes it sound like there was an MFN violation (in addition to the national treatment violation resulting from more favorable treatment for US tuna products).
But looking back to the "detrimental impact" findings, I'm not sure there ever was a comparison between Mexican and non-US foreign products. Here's the part where the Appellate Body describes the panel's factual findings, on which it relied for its own conclusions:
234. The Panel further found that: (i) "the Mexican tuna cannery industry is vertically integrated, and the major Mexican tuna products producers and canneries own their vessels, which operate in the ETP"492; (ii) "at least two thirds of Mexico's purse seine tuna fleet fishes in the ETP by setting on dolphins" and is "therefore fishing for tuna that would not be eligible to be contained in a 'dolphin-safe' tuna product under the US dolphin-safe labelling provisions"493; (iii) "the US fleet currently does not practice setting on dolphins in the ETP"494; (iv) "as the practices of the US and Mexican tuna fleets currently stand, most tuna caught by Mexican vessels, being caught in the ETP by setting on dolphins, would not be eligible for inclusion in a dolphin-safe product under the US dolphin-safe labelling provisions", while "most tuna caught by US vessels is potentially eligible for the label".
These passages seem to talk only about US fleets and Mexican fleets. Now, the relationship between country fleets and actual products of particular countries was not explored in great detail. So, maybe I shouldn't get too hung up on the fact that the discussion was only about US and Mexican fleets. Nevertheless, I'm left with a bit of uncertainty as to the basis for the apparent finding by the Appellate Body of an MFN violation. Any thoughts from readers?