I had some shrimp earlier, and I weighed it out to 170 grams. Then I cooked it, and after cooking, the shrimp shrunk more so I re-weighed them. After they were only 79 grams. Do I record the nutrition facts from the before weight or the after weight???

It does make a big difference, here is what it is before:
170 grams
140 cal
0 fat
0 carb
30 grams of protein.

After:
79grams
65 cal
0 fat
0 carb
13 grams of protein

I am hoping for the first one, but dont want to be wrong.

Are you going by the nutrition facts on the package? It will usually specify raw vs. cooked. Otherwise it's probably based on raw. First set of numbers is probably correct, though they seem unusual (shrimp typically has some fat content).

It usually says on the packet if the nutritional values are based on it being cooked or uncooked.

e.g my 1kg chicken went to around 600grams after cooking... I know, cheap chicken. So I bagged it up in to 6 100grams bags.

If I was going off of the weight of the frozen/packaged product I would be giving myself 60grams of chicken (or water even) less once cooked.

If it doesnt say on the packet, go with the cooked weight imo.

Well, it was pre-cooked shrimp. I just put it in a pan and let it heat up and brown a little with some garlic salt and pepper on it.