Brown started due to an injury to Oliver Ross. Keith didn't start until his third season in the NFL, and Sendlein I think was only a starter due to injury.
I do not this this this is the case.
Regardless, hopefully this is the end of people referencing PFF's OL "metrics" to gauge Offensive linemen. For two years before he came to the Cards, Hadnot graded out as one of the top 5 linemen in the NFL in PFF's rankings. Started for one season and was completely non descript.
Sendlein started the last two games of 2007 after Al Johnson was injured. Hasn't missed a start since. Though he did miss a snap because he was bleeding all over the football.