4
Tom Brady was backup for Drew Bledsoe in 2000 and part of 2001
Kurt Warner, Aaron Rogers
tom brady
Akili Smith. No one else
The only one I know of was Danny White (#11) of the Dallas Cowboys. Steve Spurrier was the 49ers backup QB and #1 punter for the seasons 1967-1970.
0 ... either as a starter or backup.
ELP
Favre was the backup for that season behind Don Majkowski who was injured that same season. Favre was brought in and became the starter from that point on.
Backup quarterbacks have been Rohan Davey, Matt Cassel, Brian Hoyer, Vinny Testaverde, Matt Gutierrez, and Ryan Mallett.
The San Francisco 49ers backup quarterbacks for their Super Bowl wins:Guy Benjamin (SB XVI)Matt Cavanaugh (SB XIX)Steve Young (SB XXIII and SB XXIV)Elvis Grbac (SB XXIX)
Late 60s to early 70s