I find it difficult to believe you added 100lbs to your squat LEGIT in 4 weeks. Maybe if you switched from doing real squats to quarter squats on the smith?
Deca durabolin has a decaonate ester which is longer acting and usually won't see huge gains on it in 4 wks so this sounds very unplausible at which by week 6 i would think that was all gone unless it was just a placebo effect. Are you sure it wasn't NPP