How is it interesting? Pretty simple to take a tape measure, inside or outside, measure actual, multiply 'em, divide by 1728 and you get your volume, inner or outer. What ya bought isn't what ya got. They have tons of different versions, who is to say you're looking at the same thing I picked up? Never mind if they changed anything.
This is common with these pre-made boxes, MANY are not what they're advertised for. At least with sealed it's less of a big deal. I picked up a ported box, spec'd at a 38hz tuning. Actual tuning, validated with testing, 57hz. Ridiculous difference! I subtracted port area with foam blocks to get it back to the tuning I wanted, which isn't my favorite method but it was for the commuter car so who really cares... fixed the rest of response with DSP.
I suggest you do the quick math with listed external dimensions, then derive internal volume based on expected internal dims given wall thickness and don't forget to subtract braces/dividers. If it's even close to what's spec'd, probably fine. If you end up shy half a cubic foot per driver... meh. What do you expect for the price (shipped!).
Don't get me started on TS parameters. Those spec'd by JBL are not what I tested. We have guys living and dying by model races made with averages/junk input. It's sealed, so all is generally forgiven, but I'm a test guy so I'd rather have no data than junk data. I do miss the days of believing spec sheets though, life was easier lol.