Bobby Evans played both RT & LT at Oklahoma, he's played RT, RG & LG for the Rams, he's regressed since the Packers playoff game last season. IMO, I'm not sure if it's a conditional thing, but they did not go to Allen because of Corbett at Center, they went to Allen because Evans was a turnstile at RG.
I was not happy when they went with Evans against Seattle, but they won in spite of him. Have to applaud Kevin Carberry because I was impressed he went with Edwards at LT & Shelton at LG, but to pivot and go with Jackson, who played plenty of LT for Iowa and stay away from Evans was impressive. Some assistants won't make that type of call, they will go with the guy with experience, regardless of how well he plays.