[rjsimmon]

...the USMCA acronym does not suit Mexican law, under which the trade pact would be a formal treaty, not an agreement.

So, how was it OK when it was NAFTA?

[Buckeye McFrog]

Well whaddya know. Mexican law actually respects the difference between an agreement and a treaty.

[Hugin]

The answer is right in the article...

In Spanish, NAFTA was known as TLCAN, short for "Tratado de Libre Comercio de América del Norte."