The least amount of concrete would have been poured if the driveway slabs were flat bottomed and a consistent thickness.
We must assume this as “the worse case” since the contractor would make a higher profit.

But a knowledgeable professional would have made both lengthwise and transverse “ditches” in the subsoil before the concrete was poured to create concrete “cleats” meant to help the slab resist sideways and downhill drift. Since most cracks occur near edges it is good practice to make the concrete thicker at edges, and especially at corners. On automobile driveways it is good practice to make the concrete thicker underneath where the tires will roll.

Combine these two “practical tips” and the unseen bottom of the concrete will not be “pool table flat” but rather “lock and key” hugging the subsoil.

Ultrasonic thickness testers could be used to see if this varying concrete thickness exists. Ultrasonic testers are way cheaper today than they were in the 1980s.
A cheap IR Temperature gun could also be aimed at the driveway on either a very hot or cold day. On a hot day the thicker concrete might read a bit cooler than nearby thinner. After a cool night it might read warmer.

If Superman is flying overhead just put a Lois Lane look-a-like in a skimpy dress to wave him down for a quick X-Ray vision.