Most platforms with some type of blog-like structure, like Twitter and DEV, face the problem of too many notifications. Users can have thousands of followers and even get thousands of replies on everything they post. This is exacerbated if the platform doesn't let you opt-out of notifs on silly things like "someone liked a reply to your tweet". So they usually have some sort of notification-aggregating system, where you see "Name and 7 others liked your post" instead of a separate notif for each one.
But both Twitter and DEV have a problem with double-counting in these aggregated notifs. They seem to count the number of "recent" occurrences rather than "since last view", so I'll see "15 people liked your post", then the next day "16 people liked your post", meaning 1 new person.
I've yet to see a platform that counts them since last view.