You have to remember that what we do is a performance assessment or evaluation
We are not making a condition report. Nor are we trying to assess the strength of the concrete or of the reinforcement. What we are doing is assessing how well the foundation is performing.
Consider how a mechanic might assess how well an automobile is performing without being able to see any part of the drive train
The mechanic could attempt to start the engine, run the transmission through all the gears, even check how many miles per gallon the car gets, check the wear on the tires and carefully listen to the engine and transmission as it goes through its paces. The mechanic could read the label on the vehicle to confirm the age. The odometer would give the mileage.
A skilled mechanic could make a reliable assessment of how well or poorly the car is running without looking at the engine or transmission, much less disassembling the engine and transmission. The assessment would take into consideration, the age and model of the car. The mechanic could access databases that would show what repairs had been made to the vehicle.
A structural Texas Professional Engineer should be able to provide an independent assessment of the performance without looking at the foundation
One purpose of a slab-on-ground foundation is to reduce the distress and damage to the house that would otherwise result from the swelling and shrinking soil. Note I said “reduce”, not eliminate. The assessment would have to be comparative. That is, the assessment would need to compare the performance of the subject foundation to others in the same area, age and construction.