Although Thunderbird was one of Ernest's earliest offerings after prohibition, and arguably one of the best sellers at the time - You may note on your Tbird bottle that E&J does not appear as the vintner or distributor. Even their website fails to mention TBird.
This was because of a move by the Gallo company to become more "upscale" in it's offerings. The label says it is made by "Thunderbird, LTD".
What's the word?
Here's some good Port info:
http://www.roadkill.com/~davet/portWineFAQ.html
Wine Spectator indicates that 1994 vintage is the best in recent stock.