Pharaoh vs. Pharoah

I'm aware, that Belintar is not called Pharaoh anymore, but God-King, but anyway in the Adventure Book of the Gamemaster Screen Pack, p.6, it says:

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The Stranger proved himself to be the sacral king and from then on was called God-King, or Pharoah.

I have seen this title (Pharoah) as well as its alternate form Pharaoh in several older publications.

But from my perspective - being a non-native English speaker - the latter is the correct form, whereas the former looks like a typo.

Another example supporting the assumption, that Pharoah is a typo, is Thunder Rebels. In its index you can find
 

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Pharoah .....................15, 152

but if you look at the respective pages the title Pharaoh is used!

An Internet search showed something similar: even if searching for Pharoah most results were about Pharaoh. The only real hit was Pharoah Sanders, a Jazz musician, who used Pharoah as a part of his artist's name.

So is my assumption correct, that Pharoah is a typo, or do I miss something here?