Yup, that is correct—MADHEL is the official source. The API link is essentially the back-end of the official MADHEL website, which is at https://ais.anac.gob.ar/madhel/ . I believe their Android and iOS MADHEL apps also use this API. But I am not sure about that.
While there are many positive changes happening in Argentina right now, I have serious doubts that ANAC (Argentina’s National Civil Aviation Administration) will document the API. To provide some context about this agency: it has historically been used by the Peronist youth organization “La Cámpora” as a means to place its members in well-paying positions. This practice prioritized political affiliation with Peronism over professional qualifications. As a result, much of ANAC’s staff lacks the expertise (and willingness) needed to perform their roles effectively.
As a matter of fact, I have first-hand information from a contact at a software provider for a very popular EFB responsible for the Latin American market. They told me they had reached out to ANAC several times and didn’t even get a reply. It’s worth noting that besides being unqualified—many staff members don’t even speak English—the Peronists are also nationalists who tend to view American companies unfavorably.
Hoping that they will all be fired soon, it’s clear that it will take some time to get ANAC back on the right track. Until then, don’t expect them to document the API anytime soon.