I'm not sure why I never realized this before, as I have enough Discover CLI request denial letters to wallpaper a medium-sized bathroom. I guess I've never flipped over and read the back of my dozens of denial letters. Today I did, though, at the advice of ABCD from maybe a month ago when he said if you send in a copy of your denial letter to TU they have to send you a free credit report. So, I flipped over my most recent denial letter to get the address to send it to TU and I found some other good stuff there. In addition to your TU FICO score at the time of the denial, they also provide you with negative "Key factors that affected your credit score..."
From nearly every FICO score source, I've been reading the same 2 negative reason statements related to my profile for the last 6 months or so. 1 - Time since most recent account opening is too short and 2 - Length of time revolving accounts have been established. I never get anything past these 2 codes... until now.
Discover provides 4 total negative reason codes. My first 2 that I'm quite familiar with at this point, then 3 - Too many inquiries in the last 12 months and 4 - Too many accounts with balances. I went back and looked at older denial letters from Discover today, even back when my profile was dramatically different and there are always 4 negative reason codes.
I just thought this was pretty cool, since it's often difficult to find any reason codes with > 800 scores, but never more than 2 from my personal experience thus far.