That 90 day thing may no longer be true because I was declined for Costco Amex on 3/25 and approved for Amex Platinum on 6/5 this year. Aftermath, I would just give it a go and see what's what. Good luck!
Costco (credit) and Platinum (charge) are different categories of products. I cant apply for a gold charge but was approved for Delta gold the day after hearing about 90 days.
OP, you have a Blue Cash listed in your siggy so I don't understand the grief over approving you for one of their charge products. I believe those are the easiest of all to get.
Are you on good terms with Amex with your Blue Cash? If so, call new accounts or a credit analyst and ask for a recon. The worst thing that can happen is a decline so you've got nothing to lose. Maybe offering to fax your EX CR would prove helpful. However, if your other CRs have a baddie, proceed with caution. It would be a major bummer to get initially approved only to have the new account closed upon account review.
Good luck and post your outcome.