one of the achievements is to find a certain amount of the daedric artefacts.

but how does it work exactly, do you have to actually have them in your possession/stored or just to have discovered them?

eg. nocturnals skeleton key in the thieves guild quest line. if you complete the quest and replace the key does that mean it doesnt count anymore or does it still count because you found it?
so effectively you have to get all the artefacts and not finish any of the quest lines possibly associated with them?

Hmno, you need to have had a total of 15 of those in your inventory... As whenever a Daedricartifact is added to inventory, an internal counter is incremented by 1, once that reaches 15, you get your achievement. So no, you don't have to have 15 of them with you at once, you're free to sell/lose them as you see fit. Just make sure that over your cahracter's playtime, you get to carry at least 15 different artifacts.. Note that by refusing to accept an artifact (e.g. Vaermina's quest, or Clavicus Vile's quest) means you could fail to gather 15 total.

thanks very much.

good to know i can complete quests. i dont like having uncompleted ones hanging around.