Board Thread:Legitimate Canon Questions/@comment-4467206-20161117104304/@comment-10759846-20161123090511

Because they'd just forgetting Stiles not everything that happened involving him.

Like shown episode 2 with Scott in the woods,Maila knowing someone used to help chain her up and Lydia being in love with Stiles.

Basically they have all the memories of the things they've done with Stiles but they can't remember who he was.