Well NBC asked Mushi to make all text in English and that agreement was back in episode 9 where with Gigantor it wasn't a westernized show at all in fact he coudn't get the first 26 episodes not because TMS din't think they weren't good enough like they sad first but later confirmed that tetsujin 28/Gigantor was actually a wapon designed to fight against the USA.
That was in the first 26 episodes so there was now way they could sell those to to them the begging of with is Gigantor is actually episode 27 and as to be expected started without any sign of a real begging the just made some stuff up with that in mind you could imagine that there would be Japanese text now and then.
If it would have been Mushi they might have made the text english to begin with but TMS had never considerd the possibility of selling there stuff internationally at this point.
they also where like WTF do we do now those Americans are trying to buy a Cartoon of us where America get's actually attacked

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