So I finally got the courage to try the backdoor number, got someone who was nice and polite, but didn't help me get a CLI, nor did she tell me if my account will ever qualify for one.
She asked me if I received any letters, which I have and I said so, and then she said my account is eligble for an upgrade and that the "representative transferred me to the wrong department" so she then transferred me to another department.
Which I figured that's the end of my CLI request.
Then I got another Senior CSR who asked me if I PIF every month. So I told her that I'd had this card for 9.5 years and I'd done everything from carrying a balance, to PIF every month, to currently only using every few months because the limit limits me. While I haven't asked within the last year, I have asked several times over the first 8 years and was always told my card wasn't eligible for a CLI. This CSR said she could upgrade my CLI by 10K and give me a temporary 6 month APR of 5.9% or updgrade my CLI by 15K and keep my APR at the 19.80%.
Since I now PIF I took the $15K option! It's already showing so, after being at $500 CL for nearly 9.5 years, I finally have a $15.5K CL, which puts it at my highest individual CL. I even told her that I had pretty much given up on this card, didn't intend on closing it because it's my oldest CC, but that I figured I would never get a CLI. I confirmed there was no hard pull, she just did a review of my account.
She was so nice, and helpful and I honestly was in shock because of this CLI. I didn't figure I would get one. 
So thank you to everyone who posted the backdoor numbers, and to anyone whose sitting on a card they fear will never get a CLI, try the back door.
I also got a CLI on Discover through the automated system from $6.8K to $8K.
