despite all that.... from 200g down to 130g is quite a drop.
What is the normal ratio for meat shrinkage after cooking?
Depends on the type and cut of meat, as well as cooking method.
What's sneaky here is yes it might be 200g before cooking, but there are two cooking processes. The restaurants will receive it at a lower weight already, then they cook it again.
In the case of ribs it absolutely depends on the way they cook it. There's no way to determine for sure. It does sound like a rather massive drop in weight for ribs though, as the majority of weight with ribs is the bone. There's less than half the actual weight in meat on ribs, so in order for them to have lost such weight, they'd have had to have lost 70g of the meat and a little moisture in the bone.
I highly, highly doubt it. In fact I'm happy to call bullschit on that one. They'd have lost 50-70g (depending on bone moisture) from about 100g of meat. Utter crap...