I don't think this is correct.
http://www.nrmp.org/res_match/special_part/us_seniors/match_results.html
The only way you could get the "Congratulations, you've matched" message while only matching a Prelim spot is if you
only listed Prelims in your ROL. Otherwise, you would get the "Congratulations, you have matched to a one-year position" message.
Summary: If you got the "Congrats, you've matched" message, then you've fully matched. Four years. Now you can drink.
Either way, thanks for freaking me out and killing my buzz.