A caveat - last year, I did a bunch of research on the amount of water in frozen turkeys. It ranged from about 5% water all the way to 13% (think about it, 5% of a 20-lb bird is almost a full pound of water, 13% is 2.5 pounds, so you're really getting a 19 or 17.5 pound bird) I saw that TJ's "pre-brined" was one of the ones with a very, very high percentage of water - but I wasn't able to get a snapshot of the exact percentage (yes, I did run around grocery stores one year taking pictures of the labels on frozen turkeys.)
Here's an interesting page from USDA, explaining all the terminology.
The worst offenders are turkeys labeled "brined," "pre-brined" or "marinated." Interestingly, I read here that USDA stipulates that if a meat product is cured like a ham, the weight must reflect pre-curing weight - but I don't see any regulation regarding "marinated" turkeys, quite the contrary:
Code of Federal Regulations wrote:381.169 Ready-to-cook poultry products to which solutions are added.
(a) Butter alone, or solutions of poultry broth, poultry stock, water, or edible fats, or mixtures thereof, in which are included functional substances such as spices, flavor enhancers, emulsifiers, phosphates, coloring materials, or other substances, approved by the Administrator in specific cases, may be introduced by injection into the thick muscles (breast and legs) of ready-to-cook poultry carcasses and may be introduced by injection or marinating into any separate bone-in part therefrom, for the purpose of providing a basting medium or similar function. The ingredients of the added materials and the manner of addition to the products must be found acceptable by the Administrator, in all cases. The introduction of the added materials shall increase the weight of the processed product by approximately 3 percent over the weight of the raw product after washing and chilling in compliance with Sec. 381.66. The weight of the added materials introduced into the poultry products as provided in this paragraph shall be included as part of the weight of the poultry for purposes of the net weight labeling provisions in Sec. 381.121(b).