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I seriously doubt that one credit cycle will affect anything as far as how any lender views your account - assuming that you don't continue to post a maxed out card or miss any payments.
Absolutely no need for concern if you stop using the card for new purchases. Hover over the BoA cards in my signature - the two really big ones haven't seen a swipe in over a decade and those lines have grown just in the past few years. That was one heck of a recon with NFCU, by the way. Nice job! I haven't heard of a BoA CLI being denied solely due to being under 6 months old. I've received them as recently as the past 18 months as early as 3-4 months after opening. The request you made last month... any chance you made it at the very end of the month (past 30 days)? If so, I'd call ASAP to speak with a senior analyst. It actually could be more the late showing on your report.