While it is possible for your fixtures all to be vented its highly unlikely. They would have had to run the vents back downward to the basement which would be visible as secondary pipes, or go through the second floor walls to the attic, or go through the first floor ceiling to join them all together.
There is a simple test to see if the kitchen sink if vented; Fill it with water and pull the drain plug. If air bubbles back out of the drain its not vented properly. If it drains well and fast, then you are vented. Tubs generally are self venting. Toilets are usually close enough to the main stack to be vented through the stack.
Do all the pipes disappear into the walls or do the go through the cabinet base into the floor?
I've never seen the vent pipes run down to the basement .