Around those times, Mexico was really soft regarding this type of licensing stuff. Bootleg toys and comics were rampant. One of the most popular comics of the time, Fantomas, based on the character of the same name that run for nearly 3 decades, never mind that the character was completely unlicensed.
The funny thing is that this was a serious editorial, that had the license from Marvel to publish the comics. Could they at some point started doing comics without Marvel's consent? Quite possibly, actually. As meanwhile Marvel wasn't looking, they might been fine.