Our Solera has only one kitchen sink basin. SWMBO puts a gallon in a dishpan, washes dishes in that... a gallon of rinse water in the sink basic,and that's only appx 2 gals for washing dishes.
As for showers - we installed an Oxygenics shower head with a full shutoff valve. Our procedure uses minimal water but it's better than a "marine" bath. We just wet down the body, and turn off the flow... lather up and rinse... then do same with our hair. I doubt we use more than a couple gallons per shower.
Recent trip out west we went 6 days on one tankful (35 gals per FR spec); that of course included black water use, but we used public facilities for toileting wherever possible.
My point is that one can get by with smaller tanks, but it takes practice. But the OP has a point. Whenever basic specs change it's incumbent on the manufacturer and/or dealer to inform the buyer. As to color changes, etc. it's easy to see those changes in the PDI and buyer has right to walk away if it's not what he ordered. Something like tank sizes would not be detectable. However... if you drive it off the lot, it's yours irregardless!