One way of looking at the EPR issue is ....what´s the EGT at that thrust setting, other conditions unchanged..for a brand new engine and for a 10 year old one......chances are the oldest engine will require more EGT to produce the same pressure ratios, thus, same amount of thrust...if we´re talking about identical engines, 10 years apart, then I think if 1.8 epr is achieved, thrust output will be the same.but the engine will need more fuel, more temperature to produce it....
but...I could be wrong...it´s been known to happen...