User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-5170433-20151207141753/@comment-71.50.115.82-20151207200514

Actually the 12 keys was just a thought for the gate to be opened more faster since collecting magic power takes much longer and remember that Hisui didn't use them b/c they had gathered all the magic power needed to open it. And also Layla having the keys doesn't make sense b/c if so then wouldn't she had just give all of them to Lucy instead of just 3? And not to mention on how the others like that guy who had Virgo's key, not sure if you count that filler scene but that farm place where Lucy found Taurus, Karen who had Aries and Loke's, those villagers who had Sagittarius', and Yukino who had Libra and Pisces had gotten them. Based on the fact 7 years worth of magic power is needed to open the gate, we can say that Layla has that amount of magic power and now that I think about it, in the GMG arc when Lucy was training to increase her stamina, Capricorn said that Layla was doing the same thing as well. Could it be she done it to open the gate?