The only question is how much extra water from processing the product gains during the freezing process or how much water might evaporate from the product if it is fresh.
There could have been a slight water gain in the older freezing processes, which weren’t as cold and so took longer. Today’s flash freezing should pretty much eliminate that.
I doubt that most products would lose much water by the time they get to you, although it’s a possibility for a few fruits.
Hard to imagine chicken being affected either way. I’d think that any weight differences would be negligible, even if you let it freeze in a home refrigerator and then thawed it out. It’s too impermeable.
However, some foods end up with a lot of frozen water mixed in. Open a box of frozen spinach and it seems like it’s 75% spinach and 25% ice by volume, and probably even a higher water percentage by weight.
I don’t know whether the package advertised weight is before or after all that ice is added. I know what the answer would be unless there are regs to prevent it.
But if the OP wanted the equivalent of 100g of fresh spinach, (s)he would be wrong to weigh out 100g of spinach and ice mixture.
Most meat now is flash-frozen, so external ice isn’t as much of an issue. Although before freezing the meat had gosh knows how much brine & “flavorings” injected.
I was under the impression that there was some extra liquid involved due to the amount of liquid left on a plate when you defrost meat. Then again, it’s not a great amount really is it?
Well some freezing processes might involve extra liquid, but I always thought that the liquid you get from defrosting things is just the product losing moisture due to broken cell walls. As in, you get the same amount of stuff but some of the water that was inside the fresh food has now leaked out.