This article is adequate enough to be labeled complete, but if you have additional information that you want to add, please feel free to do so.
The Hathor Curse is the curse Mine-a had cast to serve as a lesson to the Hathors present in Hathoria that time. She cursed them to have a hideous appearance and when they die, no bodies will be left for their relatives to lament on.
After Pirena re-established Hathoria and became the queen, she probably asked her sisters to uplift their mother's curse to those who got afflicted that's why the soldiers looked normal once again. (Except for Hagorn as he retained his cursed appearance.) Although she reinstated the curse to those Hathors who turned their backs on her to join their former leader, Hagorn.
Ynang Reyna Mine-a
"Isinusumpa ko sa oras na kayo ay mamatay, kayo ay maglalaho at walang bangkay na matitira sa inyo upang paglamayan ng mga mahal niyo sa buhay. Isinusumpa ko rin na mawawasak ang inyong kaharian. Ipinapalangin ko sa apat na mahahalagang brilyante na ito na gawing kahindik-hindik ang inyong mga wangis upang kayo ay layuan at pandirihan ng lahat ng mga mamamayan dito sa Encantadia. Isinusumpa ko kayo!"
It seems those afflicted with the curse were only the Hathors present in Hathoria when Mine-a had cast the curse and not the entire race of Hathors. This explains why Gurna and Pirena's bodies did not disappear when they died and when Mira was born she did not have a hideous appearance. This is the best assumption fans can assume.
Episode 13-14 the curse has already been cast yet there were a lot of Hathor remains during that battle. Supposedly, the bodies disappear the moment they've been killed.
In Gurna's case, her body was left lying at the boulder the moment she died instead of vanishing immediately the assumption could be accurate then but, she was afflicted with the red marks appearance part because when Hagorn asked her why is she hiding her identity as a Hathor when she is already at Hathoria then the markings appeared on her face.
Hagorn's body did not disappear after being killed by Raquim. The markings on his face when he was locked up wasn't removed indicating the curse is active on him.