tl;dr: You can add those pages on your profile at "Manages ..."
On the most recent interface some pages might not have the option to edit Team members. For some of my older pages the Team Members section is available, for newer it is not there (regardless the like count). Interesting that it shows up in the Page Admin app for every page, but not in browser.
Older page with 1 like:
Newer page with ~30 likes (it is not even available in the Edit Page section)
You can still add yourself by going to your profile. If you have pages you already manage, there will be a "Manages ..." section where you can add pages. You cannot add others, though, but I think it was never an option.