650kgs would have been the liveweight. Dead weight of an Angus x heifer would be likely to be around 350kgs - unless she was the size of a mammoth!
The proportion of meat you get back from a given deadweight depends on a lot of factors. How much fat has been trimmed off, how many of the bones have been removed, how much weight has been lost in hanging (more hanging = more drying out = less weight, plus very long hanging times may cause some discoloration in lean meat, requiring more trimming, so even more weight lost.)
In your case, if it was indeed not hung but vac packed straight away, then you wouldn't have lost weight through drying out. But if all the bones have been removed, then there will be a considerable loss of weight - my butcher was telling me he lost a significant proportion of the weight of a Shorthorn bullock as its bones were so thick.