The DMCA takedown notice must meet each element as specified by law. In particular, the notice must explicitly identify the copyrighted work as well as the material claimed to be infringed.
In their DMCA notice, LV failed to meet the requirements for a valid DMCA takedown notice. By failing to specify their own work, as well as what materials in particular were allegedly infringing, they ensured that their claim was invalid on face.
As a result, LV isn't going after anyone. An invalid takedown notice carries no duty to act on the part of the service provider. It, quite simply, doesn't exist. The really remarkable thing here isn't that LV filed an invalid notice--it happens all the time, particularly when they're automated in other circumstances--but that Github acted on it at all as an invalid takedown notice is not considered by the courts to impart actual knowledge of infringement.
In effect, if it's invalid, the takedown notice doesn't exist.
Sadly, no. I'm mostly going off Allan's comments on the DN thread where he talks about them using their illustrations.
And also than they haven't been running around issuing DMCA's to every _other_ flat UI style everything.
Clearly, they believe specific assets were copied to the point that a DMCA was appropriate. Pending a full post from LV, I'm giving them the benefit, as I'm certainly not giving the benefit of the doubt to the designers who so thoroughly ripped LV's style.
Should that post never come, or its contents show LV as trying to enforce a copyright on something that was merely "inspired" and not copied, I'll change my tone.
It doesn't matter. A valid DMCA takedown notice is fully self-contained. There's no follow-up, no sending someone to a blog post, or anything else. If it's not in the takedown, it's not material to the claim.
Refer to Perfect 10, Inc. v. Google if you're curious.
You're jumbling what LV actually did with the simplification of what they did.