The Relationship of GATT Article III:4 and TBT Article 2.1

This is from the second EU written submission in the Seal Products case:

The legal standard under Articles I:1 and III:4 of the GATT 1994 and Article 2.1 of the TBT Agreement with respect to their non-discrimination obligations is fundamentally the same

In support of this view, the EU says:

345. Therefore, the national treatment obligations of Article 2.1 and Article III:4 are "built around the same core terms". The contours of the basic nondiscrimination obligations in Article 2.1 of the TBT Agreement and Article III:4 of the GATT 1994 are similarly crafted as there would be no point in recognising the regulatory space in the TBT Agreement if then the same regulatory autonomy were to be undermined under Article III:4 of the GATT 1994.

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350. ... the list of exceptions under Article XX of the GATT 1994 is exhaustive whereas the list of objectives that may be legitimately pursued by technical regulations is merely illustrative. If both the GATT 1994 and the TBT Agreement are intended to strike a balance between trade liberalisation and regulatory autonomy, then it makes little (if any) sense for technical regulations to enjoy a much broader scope of policy space than all other types of internal regulations.

The EU acknowledges the Appellate Body's statement in US – Tuna II (Mexico) that the "scope and content of [Article 2.1 and Articles I:1 and III:4 of the GATT 1994 are] not the same."  What did the Appellate Body mean by this?  How different are these provisions?  What further clarification will the Appellate Body offer us in the event of an appeal in the Seal Products case?