I got that same letter after being 2 hours late. I called the magic number at the 6 month mark and got a $500 increase to $800. Don't say how much the letter stated...
Got a $300 auto CLI on third statement a few days ago, with a $179 balance out of $200. I make decent payments ($60-$90), never PIF and always carry a high balance.
I have two Red cards, opened a few days apart. I also work at Target and I was told everyone gets a pre-approval if they spend $50 or more using a CC...