Would it have anything to do with Border's having finally closed their doors?
Borders only accounted for something like 8 percent.

This is just for one of my publishers (I currently have three).

But if Borders is the only chain carrying the book(s), like in my case, the drop off was significant. Like, the numbers are REALLY, REALLY SAD! August and the beginning of September look great, when everything went on sale and whatever they had stocked went out the door. But now... ugh.
Did you have an abrupt drop from last week to this or a slower decline?

I just wonder if there is an inaccuracy. Esp. since no drop off in one of my titles.
I will use 100 as an easy number to work with for a starting point the end of Aug/first of Sept. and use the percentages I can easily calculate in the differences each week to illustrate what happened to mine.

One of my slightly older titles:

100 - Sept. 4
92 - Sept 11
69 - Sept 18
21 - Sept 25

And another one:

100 - Sept 4
66 - Sept 11
71 - Sept 18
15 - Sept 25

I think Borders was better about letting stock sit on shelves rather than returning it. So, in my case, those books got picked up when they went on sale. I think B&N returns stuff, and doesn't let it sit there more than a few months. Thus, I have far fewer books on B&N shelves to sell. And I don't know that indies pick up my YAs much.
Here are my numbers, using 100 as equivalent to the number sold on Sept 4

One title
100 - Sept 4
78 - Sept 11
113 - Sept 18
150 - Sept 25

Another title
100 - Sept 4
146 - Sept 11
106 - Sept 18
4 - Sept 25

Could that all really be from Borders? They've been shutting down for a long while. Or maybe it reflects returns from Borders???
I just did a search on twitter using "bookscan" and a few others are talking about it.

Here's one tweet: PVBrett Bad week. RT @awfulagent not a lot of fun looking at Bookscan #s this week, first post-GoB sales at Borders, many books dropping by 50%-90%.

So yeah... I think it's Borders.
But Borders accounted for 12% of most book sales. (I googled it.) They must have accounted for a lot more of Bookscan's numbers.
Yes, that is what I'm thinking. Because Bookscan doesn't include grocery stores, Target, Walmart, etc. but that 12% would include all of that. And for me, I'm not in any of those places, but I was in Borders, so take that away from me and you've taken away half or more of my hard copy sales.
My drop off wasn't the week of 9/12, rather the week of 9/19 (the numbers just posted). That latter week reported sales 6% of the prior week. Gulp.

I hope this isn't what the post-Borders world looks like!
That is actually the same week - I'm just using the beginning, you are using the end date.

I'm wondering if there is an error?
Aaaand, if you look at where I was this time last month, I am at 15% of that now. Wah.
I just wonder if it's wrong. One of my books is up a bit, the others seem to be down by an amazing number, like cut by 95 %.

It's either Borders or a mistake.
See, one of my books went up, but others went down so far it's crazy. Never have had a week like that before.
I'm hearing this from about 90% of people. So we're all in the same boat. It just seems too huge to be Borders. I wonder if there's a mistake?