The Tiguan stated 600+ litre size is with the rear seat fully forward, its lots smaller with it right back.
But yes, giving a litre amount is a bit silly, given it could be with or without a boot floor (sold with boot floor, measured without…) or seats moved or measuring every nook and cranny using the 3d model of the car despite your dog/suitcase not having the same level of strange nooks and crannies to fit the car…
Looking at some magazine/online reviews can be good as they use a standard flight case and give the total that fit, both a useful measure of size and uniformity of the boot.
I have used a Swedish car magazine, ViBilagare, they are pretty stringent in their tests & I can scan through back issues with my Readly account. I also like them as they test how good the headlights are (and give a graphic of the light pattern/cutoff distances.
In life, it's not who you know that's important, it's how your wife found out.