First question is if im leveling an artifact, and say i need 2000xp to reach a milestone, but i use 10000xp, do i lose that extra 8000xp or does it carry over after breakthrough? Second question is when buying the say rank 160 catalyst pack or whatever its called on the marketplace, does that literally only have the cats needed for rank 160? or does it have all the catalysts for every milestone up to 160 as well? Does it include nth metal to level the artifact up or is it solely the catalysts?
The extra XP appears to wrap over once you breakthrough. The amount of splash over XP I've tested was much smaller though. From: https://forums.daybreakgames.com/dcuo/index.php?threads/rank-160-catalyst-pack.299862/ Just what is needed to breakthrough at 160.
Coffee is correct(should I call you Coffee? Or do you prefer something else?) The XP carries over. The only time I'm not certain of is when you hit 160, I don't have anything over 120 atm...
To answer your first question, any excess XP carries over after breakthrough, even at rank 160. You can verify this yourself by checking the total XP which your artifact has when you hover the cursor over your artifact.
You'll never lose an XP if you go over. No matter what the amount. When they first released the Augments I didn't know what the hell I was doing. And hit the wrong stacks and went way over the amount needed. The Atlantean Episode saw an increase of how much you could have in each core. I only had to add about 20 Exos to max it out again.
