Why 1 in 13?

But if the orcs have the blood of Adar, would it be because of Morgoth's magic?

Adar stated there were originally 13 elves who were taken by Morgoth to be tortured and deformed into orcs. Those 13 orcs were the mothers and fathers of the entire race.

Just to be clear, Adar and his whole backstory were invented for TRoP... the story is based on some ideas implied by what Tolkien wrote, but specifics like 13 elves and Moriondor were never mentioned.

It is one of the cool ideas from TRoP, but I wish it could have been introduced without so much lore breakage.

I'm aware of that, that's why I said Adar told that story instead of stating it as definitive.

But since you never said Adar was non-canonical, someone might have thought Adar was canonical and what he said could be then as well.

I have to say that I am beginning to have issue w/ canon v non-canon when it comes down to non-canonical content presented in a completely non-canonical platform.

When Galadrielle mentions Adar's offspring, I can't understand if these are her real children or a laudatory term?

I mean, you'd basically have to want them to be his real children to believe it... there isn't much evidence or reason to think they would be his biological children, but maybe some kind of descendant, if you were to believe the backstory.

@15ichigo99 do you know what it means for Adar to have been "born" in the First Age in regards to the time frame of TRoP?

@Fandyllic ,I guess that makes him old.

Good question, I think it might be both. Many are probably descended straight from him, while others might be from the other Moriondor