CITES Resolution 16.8 itself uses "passport" to describe the musical-instrument certificate

Paragraph 1(g) of CITES Resolution Conf. 16.8 (Rev. CoP17) recommends that "the Parties concerned treat each musical instrument certificate as a type of passport that allows the non-commercial movement of the identified musical instrument across their borders." The same paragraph specifies the procedural mechanism that makes the metaphor literal: a border officer "inspects the original and validates it with an ink stamp, signature and date to show the history of movement from State to State," and critically "does not collect the original at the border, but allows it to remain with the specimen" — the document travels with the instrument the way a passport travels with its holder, rather than being surrendered or re-issued at each crossing.

This confirms that the "passport" language in claim-cites-musical-instrument-passport-certificate is the treaty body's own chosen framing, not a journalistic simplification laid on top by secondary coverage. The distinction matters for sourcing discipline: a metaphor invented by a trade publication would be an editorial gloss; a metaphor written into the operative text of a CITES resolution is part of the mechanism itself.