Number of items not appearing next to items

1P_Rob the problem with standards is that there are way to many of them 😊 - https://xkcd.com/927/
All your examples are kinds of item counts but with different use cases. The Finder uses a status bar that not only shows item counts but free space available too. It's like those status bars in editors or word processor that show cursor position, word counts and so on. Mails counters at the top of the list are another kind of status bar showing all mails and all unread mails next to each other.
Another approach is used by Notes, Mail, Devonthink and several other applications that have item counts in sidebars. Their implementation and style is very similar although the count shown is not always a simple item count. In Notes it shows the number of item in a group, in mail it's the unread mails.
I haven't found item counts in Contacts.
In 1Password item counts would fit quite well into the Notes/Mail approach. Maybe the new appearance preferences category could get a show/hide item counts checkbox😉