The Broncos last missed the finals in 1991 when it was a top five. They came 7th winning 13 out of 22 matches. They were a much better side than the current broncos team, they just had a bad run with injuries and rep duty the middle of that year.
The 1991 side included the likes of Alfie Langer, Kevin Walters and it was the last year of big Gene Miles who did not play in their first title of 1992.
2003 is actually the Broncos worst season to date even though they made the finals. They won only 12 and lost 13 (including finals), the only season the Broncos have lost more games than they have won.