I'd say it depends on what do you mean by a concept?
I mean... There are themes and plot points and fandom clichés that can be widely used by everyone. They're not really owned by anyone and as such are free for grabs.
For example there are countless AUs with Sesshoumaru as a CEO in them, many of which also feature Kagome as his employee.
There are several canon fics in which Kagome and Sesshoumaru are magically bound to one another (personally guilty of that one).
There is the biting mark or mating mark, or Sesshoumaru's fluff being his tail and Kagome's remarkable tendency to give birth to full demon babies.
There are countless concepts like these that are being used throughout the fandom.
I would personally say it would be difficult to lay claim on a concept, because really, if you think about it, it's probably already been done by someone (although not the way YOU want to do it, which is the beauty of writing!).
But if you want to be safe, then of course it's best to ask the author in question, but if you can't remember who that was, maybe you could include an A/N at the start of your fic saying you remember the concept being used in a story and apologize you can't remember which one? Giving them credit that way whoever they are? I'd imagine them to be less offended that way if they chance upon your story.
That's my two cents, in any case. ^^;
Edit: (Or then never mind me if I completely misunderstood what "concept" referred to here... I'm just gonna go now.

*fades back to the background*)