I credit everything, regardless if it's for ct-duties or just personal scrapping. Now linking is a different thing. I usually TRY to link whether it's ct or not, but sometimes, if I can't find that designer because they store hopped, retired, etc, I don't bother looking for them.
Why do I do it, even if it is just a paint splatter or something minimal? If I look at a layout, I want to know where/who created the kit, element, paper, alpha, etc so I know where I can buy it myself. So when I use something I'll generally put the credits such as
template by . . .
kit by . .
kit name by . . . (greenery)
kit name by . . . (purple flower)
alpha/kit name by . . . (titlework)
Just so that it's broken down and people can know what I've used from what kit.
I also have been VERY guilty of creating elements/alphas from my own designing knowledge and don't credit that I've made that item to coordinate with the kit. It's just something that I never really thought about doing until your post :shh
But for the most part, I mainly stick to one-two kits by the same designer because I'm a lazy scrapper
