Replying to myself again. Thanks to a post by @bouteloua I found the critical workaround to exclude Unknown place/date, making a much smaller, maybe even manageable pile!
Tack this onto your Casuals url of choice, forcing it to yield only things in the World in the last century or so:
&place_id=97394%2C97393&d1=1900-01-01
…Oops no, I misread and the placeid’s above do not capture “The World”, only North America and Oceana. How to widen the scope to include the whole globe?