Many doctors use a guide called the Knee Society Score to measure outcomes or "success" after a total knee replacement (TKR). Points are given for pain, range of motion, and knee stability. There's a separate score for function based on the ability to go up and down stairs and walk without help.
The scoring system is set up so that age or a medical condition won't affect the rating. This is especially important for the patient who has good range of motion on the operated leg, but pain and stiffness on the other arthritic side.
Doctors may label a TKR a "success" based on X-ray findings that show the implant in good alignment. If the patient doesn't have pain and doesn't mention the stiffness, the same "success" rating may be given.
There may be a treatable source of your knee stiffness. Perhaps a rehab program beyond the TKR exercises is needed. Make an appointment for a follow-up visit and ask your doctor to re-evaluate your results.