Soviet Life Magazine for example was printed and sold in the US by the Soviet Embassy.

It might have been allowed under a bilateral cultural agreement between the US and the USSR.

That makes me curious about the details; it's worth noting that the Soviet Embassy's physical location would be Soviet sovereign land that is licensed to them by the US so long as they are allowed to maintain an embassy presence. If people go onto the embassy to buy the magazine, they are literally traveling to a foreign country to buy it.

I don't really know the exact legal situation surrounding this, but the viewpoint that in the past Soviet propaganda could be freely distributed in the US a rather curious viewpoint. The US government spent decades chasing down (alleged) communists, both using hard power and soft power, and many were effectively silenced, and many more never even dared to speak up.

So whatever the exact legal situation was the time, a free speech utopia where even enemies of the US had free reign did not exist. De-facto free speech was significantly more restricted on this topic.

That something is allowed doesn't mean that it's guaranteed in the constitution.

In that particular case, it was a result of an agreement with the Soviet government that allowed us to publish Amerika magazine in the USSR.

https://en.wikipedia.org/wiki/Amerika_(magazine)