Started dog= a dog that will pick up the birds he/she sees; may or may not be steady
Seasoned/Senior Dog= a dog that handles, should be steadied, capable of multiple retrieves with great success.
Finished dog= You will never know they are in the blind until you send them. People ask in amazement "how did you do that".
The only difference in a meat dog and a trail/test dog, is that the owner choose to or not to run the trail/test. Now a good trail/test dog versus one that does not excel in the trail/test arena could mean merely inches. This is all assuming that the dog is well trained.