potential difference between emitter-base and collector base constant, i.e 0.6 or 1.2v approx?
Your answer was for a specific load (voltage and resistance) and drive current. Depending on the circuit, the collector-base voltage can go from the collector breakdown voltage to about -0.6 volts or less. The first level occurs when the input base current is zero and the collector is at breakdown, and the second occurs when the transistor is in hard saturation, with a Vce on the order of 0.1 volts. Since in some high base-drive situations the base-emitter voltage can get larger than the nominal 0.7 volts, the voltage difference can be greater than 0.6 volts.