My bill just closed. This note is on it as a change to my cardmember agreement:
This fee is on the Rates and Fees Table on page 1 of Part 1. For Basic Card Accounts opened on or after August 17, 2023: Each Additional Platinum Card is $195 annually, and each Companion Platinum Card is $0 annually.
For Basic Card Accounts opened prior to August 17, 2023:
If you were notified of a change to the Annual Fee for Additional Platinum Cards, each Additional Platinum Card is $195 annually and each Companion Platinum Card is $0 annually, beginning on the date specified in the notification.
If you were not notified of a change to the Annual Fee for Additional Platinum Cards, we will charge $175 annually for up to 3 Additional Platinum Cards, $175 annually for each Additional Platinum Card after the first 3, and $0 annually for Companion Platinum Cards. We will notify you if there will be a change to the Annual Fee for Additional Platinum Cards on your account in the future.
So I wasn't notified. At least, if I was notified, I don't know where.
This whole note suggests that my account is grandfathered in, at least until I'm notified. I think my AUs renew in October.