Barclays card lifetime limit data point:
I tried to add an AU to my Barclays card today. I tried to add online, it asked me security questions from my credit report, claimed I had answered incorrectly, and to call in. I repeated a second online add attempt with similar result: different security questions, but still failed to add.
I called in. CSR#1 tried to add, it didn't work. CSR#1 patched in account security, who security verified me. Account security tried to patch me back to CSR#1, but I ended up with CSR#2, who claimed erroneously that she needed me to provide the SSN to add an AU. I told her I didn't have it, and that I'd get it and call back. She said she'd notate my file to reflect the situation.
Across Old Company, New Company, and private sales, I had a total of 39 successful AUs on this card. I also had one failure to add an AU due to some fraud issue (I think Barclays had put a fraud alert on my card at one point). If you include that last AU, that means that for me the total lifetime limit on Barclays was 40.
...
My plan (as mentioned earlier in this thread) is to apply for a new no-fee Barclays card, wait for my last successful AU to fall off my existing card, then close the old card and transfer the credit limit to the new card. I had a $95AF-waived-the-first-year card with Barclays that was seasoning, but they refused to let me downgrade to a no-fee card, so I closed that one.