Password Sharing Breaks Password Syncing

I recently migrated to Apple's Passwords app. Passwords synced fine across my three Apple devices (not counting my watch). I then set up a password sharing group on my Intel MBP running Sequoia. I selected all of my 300+ passwords to be shared—or so I thought; more on that below. My passwords continued to sync fine between the MBP and my iPhone running iOS 18. My third Apple device is a 2017 iMac running Ventura which cannot be upgraded further. After creating the shared passwords group, the iMac only shows four or five passwords. On a hunch, I discovered that those four or five passwords are ones that I inadvertently omitted from the password sharing group. It looks like the shared passwords won't display on this older Mac. Turning iCloud password syncing on and off and restarting haven't helped. Ideas, anyone?