SCM and GATT Article XX--a quick question

I know that Simon and others have discussed the question of the applicability of GATT Article XX to provide an exception to prohibitions in the SCM Agreement, for example here.  Why is this issue not resolved by SCM 32.1, which states "No specific action against a subsidy of another Member can be taken except in accordance with the provisions of GATT 1994, as interpreted by this Agreement." (footnote omitted)  The plain meaning of this language seems to be that  no action may be taken against a subsidy if the action is not in accordance with GATT.  Therefore, if an Article XX exception is available, there can be no action under the SCM Agreement.  It's not that the SCM is necessarily lex specialis--it is that it is, in the language of Art. 32.1, an interpretation of GATT.