Back in 2002, K-Mart went bankrupt and was at Caa3 shortly before they went bankrupt (The day they went bankrupt they were downgraded to C which stands for default). They also had their ratings downgraded twice in a very short period of time.
Sears Holdings is now at Caa3. They also have had their ratings downgraded twice in a very short period of time (even though it was months in SHLDs case, it was days in K-Marts).