How accurate are Rick Riordan's portrayals of ancient myths?

Question

The story of Cadmus and Harmonia as presented in Rick Riordan's Percy Jackson's Greek Gods, is unique in claiming that Harmonia became mortal:

Cadmus wasn’t sure he should be stealing the dragon’s dental work, especially if he was already on Ares’s naughty list, but he did as Athena commanded. When he was done with his tooth farming, a bunch of super-elite skeleton warriors sprang from the ground, and these became the first soldiers in the new Theban army. Cadmus built his city. For a while, everything was copacetic. The gods even granted him a minor goddess for his wife—Harmonia, who was a daughter of Aphrodite and Ares. Harmonia became mortal to share her life with Cadmus, which was a pretty big honor.

_{"Ares, The Manly Man's Manly Man", Percy Jackson's Greek Gods, Rick Riordan}

I realize Mr. Riordan's books target a younger audience, and this may seem like a minor detail in the grand scheme of making the myths accessible to youngsters. However, I feel it's a rather important one as Gods (and other immortals) turning into mortals is not something that happens in Greek mythology. The only story I know of that comes close is Castor and Pollux, yet not close enough, as the twins alternate between mortality and immortality. As for Harmonia, I checked several ancient versions of the myth, and she remains immortal in all.

Has Rick Riordan ever commented on how accurate his portrayals are intended to be? And given that several of the stories he presents may differ significantly from source to source, has he ever provided a list of sources he used in his research of the myths?

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_{This was inspired by a Mythology Stack Exchange question: Are there any Greek myths of a god permanently turning into a mortal as punishment?}

Answer 1

Rick Riordan in an interview says that he attempts to create a "Modern Mold" for the characters. He credits many of the stories he uses to Tales of the Greek Heroes by Roger Green. (Wikipedia). He also uses The Theoi Project as his "fact checking", which was the same source you used coincidently. (Wikipedia) Since I could not find an interview on the specific example, my guess on why he changed would either be because he wanted it to be more relatable to the audience, or he learned it and preferred it that way.

I had this issue over Rick Riordan's writing a couple of years ago, they did not match up with the information that I knew. One of the main issues with fact checking Greek mythology is that there was no original source. (per history.com). Fact checking the bible to stories is easy, we have the bible. There were many variations on all the Greek Mythologies. Robert Graves said that:

“Myth has two main functions, The first is to answer the sort of awkward questions that children ask, such as ‘Who made the world? How will it end? Who was the first man? Where do souls go after death?’…The second function of myth is to justify an existing social system and account for traditional rites and customs.”

That being said, it would be logical for there to be discrepancies throughout the stories: as long as the important moral or explanation stands, the people were free to change it as they saw fit. Thus in Rick Riordan's case, the important part was that the two got married; even if he took some liberties with the story, it can still be considered the same myth as the one we are used to.