How can I prove that Vce saturation lies below .2V?
**if you want to estimate Vce with a part number, it is helpful to use Vce(sat) @ Ic=10*Ib then go from there.
The hFE declines to about 10% of the max linear value at the rated Vce(sat).  The Vce(sat)/Ic = Rce is a computed term that is often useful to know for a switch characteristic when choosing a device or a collector load. Rce decreases with increasing  base current and collector current when saturated.
The actual Vbe depends on these values and could be 0.6V if Ic is 1mA and Vce=0.06V.
You can also see Rce (typ) @ 25'C  at full saturation with Ic/Ib=10 for this part;
Rce=60 Ohms @ Ic=1 mA   Vce= 60mV.
Rce= 5 Ohms @ Ic=10 mA   Vce= 50mV.
Rce= 1.3 Ohms @ 100mA    Vce = 130mV.
Rce = 0.8 Ohms @ 500 mA  Vce= 400mV.
This trend is common but the ohmic scale reduces for higher power switching transistors.
2N4401 example General Purpose Small signal TO92

When operating in the linear region the collector is a high impedance current sink.