I really had not considered it until a couple of days ago, but it was possible the tarp he purchased was a replacement for one he already had.
For example, I don't know, but I might have an unopened tarp/dropcloth in my garage now. So, for whatever reason, he bought one for a completely innocent reason last December, but never used it.
Now, he thinks he might like to have another one to line the trunk of his car, you know, to catch gasoline spills and bodily fluids. So, he buys one, and uses it and tosses it along with all the other stuff, and there is still a new one, in a different store bag, in the garage.
Who's to say the tarp we see in the picture is the exact same tarp he bought on the 11th?