Spanish to English Social Sciences History Spanish colonial trade

I'm translating an article about trade between Spain and Peru in the 18th century. It contains the following section title:

Comercio oficial y comercio encubierto

I've considered various translations: Unofficial, covert, underground, clandestine, undercover, etc. This is NOT a matter of contraband, black market, smuggling; it is just merchants and buyers from Cádiz and Lima getting together unofficially and making their own contacts and arrangements ("networking," if you will) as opposed to arranging things officially through the Spanish government and the merchant guilds (Consulados).

The section is introduced in the final sentence of the previous section:

Como resultado, parte del comercio transatlántico pasó a realizarse de forma encubierta.

My provisional translation (which I admit, I like the sound of!) is:

As a result, part of that trade went underground.

(Note: I had used "transatlantic trade" in the previous sentence and didn't want to repeat it.)

Which of my options do you think is best? Or, do you have another that you believe is better? Remember, it has to pair well with "Official Trade." That term is pretty much fixed.

I'm really looking more for opinions and corroboration than solutions, but whatever you want to say on the subject will be welcome. I need some colleagues to talk it over with!

Thanks in advance.