The maps at https://www.atacarnet.com/sites/default/files/documents/airp... and https://www.ana.co.jp/en/jp/guide/prepare/airport-guide/inte... say otherwise.

Immigration (can you enter) --> international baggage claim --> customs (can your stuff enter) --> transfer bag drop.

edit: Same setup for Boston, it seems?

https://www.jal.co.jp/jp/en/inter/airport/bos/info/

Immigration: "Customs declaration form - not required"

Then baggage claim, then...

Customs: "Please show your passport and customs declaration form. (Your customs declaration form will be collected here.) If you have any items to declare, please declare them to an official."

I do kind of recall the last US airport I went through internationally that there was weirdly no customs lanes or anything after baggage claim, just big one-way doors.

Not that you can reach that point without stating your declarations on the record. I think it was one of the kiosk stages.

I really don't recall anyone standing at the spot labeled customs on that first map. Although I do recall lots of k9 handlers walking around, presumably to catch anyone that didn't declare their food/drugs/cash.