"My ob will become c1"....what do you mean by that?
Even if you close the 1 Cap 1 acct, it will remain on your report & the acct will still be factored into your aaoa for at least 10 years. The one thing that will no longer be factored in, is the $600 will no longer be factored into your overall available credit. That # will drop by $600 when you close the card.
AAoA (as seen by FICO) includes ALL OC accounts, whether opened or closed, good or bad, charged-off, not charged-off, paid, unpaid, duplicate, not duplicate, etc. Basically all accounts listed on your Accounts page are included in AAoA. AAoA excludes CAs and PRs.