> For example, on https://github.com/gap-system/gap/pulls it says "Pull requests 78" in the "tab list", but the PR list view reports "35 open" (the number 78 is correct, and confirmed by e.g. `gh pr list`)

Surely a scaling hack where they use "estimation" queries that return "kind of right" results instead of 100% correct data, as it's less load on the infrastructure. Not necessarily a bug as much a shit choice from product perspective.