Deliberate mistake: There are no yellow/amber lights as Patrick drives Sam and Charlie through the tunnel. Yellow/amber lights are present as soon as drivers enter the tunnel - a warning to slow down, as well as help drivers' eyes to adjust to the light level inside. I presume it was better to have all white lights while filming (and traffic was controlled). (00:27:33)
Deliberate mistake: In "Do You Hear the People Sing?", Grantaire can be seen hijacking the funeral carriage but when the insurrection starts, he is at the tavern with some girl and Marius acts like he wasn't just there. George Blagden who portrayed Grantaire didn't want to be left out of that great set-piece so he was allowed to participate and the director must have thought no-one would notice him.