Last coach I remember having different starters was Pelini. Solich obviously didn't have different starters and I'm not sure TO ever had a different starter since 1994.
Not sure how far back in history we're going, but I don't think that matters because all that matters is Frost's history and I don't believe he had different starters at UCF.
off the top of my head:
2017 - same starter all year (POB played second half of Minnesota)
2016 - backup started two games (Fyfe)
2015 - backup started one game (Fyfe)
2014 - backup never started (Fyfe?)
2013 - backups started most of the season, third string played a ton and had one start (Armstrong and Kellogg)
2012 - backup never started (Kellogg?)
2011 - backup never started (Brion Carnes)
2010 - backup started twice (Cody Green)
2009 - backup started twice (Cody Green)
2008 - backup never started (Pat Witt)
2007 - backup started last two games (Joe Ganz)
2006 - backup didn't start (Ganz)
2005 - backup didn't start (Harrison Beck)
2004 - backup didn't start (Beau Davis?)
2003 - backup didn't start (Joe Dailey)
2002 - backup didn't start (Mike Stuntz?)
2001 - backup didn't start (Lord)
2000 - backup didn't start (Lord)
1999 - backup took job and started (Crouch)
1998 - backups played most of the season (Crouch and Cristo)