It seems like it is all stocks that are covered by
Post# of 36728
"NSCC-2013-13
To discontinue the Stock Borrow Program. (December 10, 2013)".
I haven't seen anything specifically spelled out in the 3 pdf files I looked at:
1) a7676-1.pdf,
2) SR-NSCC-2013-13.pdf,
3) SR-NSCC-2013-13.pdf-approval-notice.pdf.
My best guess is that it covers all stocks, those under $1.00 included.